By default commands such as "ctest" would not look for certificates
at all: <https://issues.guix.gnu.org/issue/37371>.

This changes CMake such that commands honor SSL_CERT_FILE and SSL_CERT_DIR
as well as /etc/ssl/certs.

--- cmake-3.13.1/Source/cmCurl.cxx	2019-09-10 17:27:36.926907260 +0200
+++ cmake-3.13.1/Source/cmCurl.cxx	2019-09-10 17:52:35.475903919 +0200
@@ -2,11 +2,8 @@
    file Copyright.txt or https://cmake.org/licensing for details.  */
 #include "cmCurl.h"
 
-#if !defined(CMAKE_USE_SYSTEM_CURL) && !defined(_WIN32) &&                    \
-  !defined(__APPLE__) && !defined(CURL_CA_BUNDLE) && !defined(CURL_CA_PATH)
 #  define CMAKE_FIND_CAFILE
 #  include "cmSystemTools.h"
-#endif
 #include "cmStringAlgorithms.h"
 
 // curl versions before 7.21.5 did not provide this error code
@@ -30,6 +27,19 @@
     ::CURLcode res = ::curl_easy_setopt(curl, CURLOPT_CAINFO, cafile);
     check_curl_result(res, "Unable to set TLS/SSL Verify CAINFO: ");
   }
+
+  /* Honor the usual environment variables.  */
+  else if (cmSystemTools::GetEnv("SSL_CERT_FILE", e)) {
+    ::CURLcode res =
+      ::curl_easy_setopt(curl, CURLOPT_CAINFO, e.c_str());
+    check_curl_result(res, "Unable to set TLS/SSL Verify CAINFO: ");
+  }
+  else if (cmSystemTools::GetEnv("SSL_CERT_DIR", e)) {
+    ::CURLcode res =
+      ::curl_easy_setopt(curl, CURLOPT_CAPATH, e.c_str());
+    check_curl_result(res, "Unable to set TLS/SSL Verify CAINFO: ");
+  }
+
 #ifdef CMAKE_FIND_CAFILE
 #  define CMAKE_CAFILE_FEDORA "/etc/pki/tls/certs/ca-bundle.crt"
   else if (cmSystemTools::FileExists(CMAKE_CAFILE_FEDORA, true)) {
libusb.scm'>
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</td></tr></table>
<div class='path'>path: <a href='/guix/log/?id=32da38d5721663a470b335f86b67cffdc4f34f0a'>root</a>/<a href='/guix/log/gnu?id=32da38d5721663a470b335f86b67cffdc4f34f0a'>gnu</a>/<a href='/guix/log/gnu/packages?id=32da38d5721663a470b335f86b67cffdc4f34f0a'>packages</a>/<a href='/guix/log/gnu/packages/libusb.scm?id=32da38d5721663a470b335f86b67cffdc4f34f0a'>libusb.scm</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/gnu/packages/libusb.scm?id=32da38d5721663a470b335f86b67cffdc4f34f0a&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2018-03-29 17:34:41 +0200'>2018-03-29</span></td><td><a href='/guix/commit/gnu/packages/libusb.scm?id=5576cfabf3485e0cf794cc3de085a3578151ee64'>Merge branch 'master' into core-updates</a></td><td>Marius Bakke</td></tr>
<tr><td><span title='2018-03-29 12:26:38 +0200'>2018-03-29</span></td><td><a href='/guix/commit/gnu/packages/libusb.scm?id=017bffc1a352599c5468f10cf4ef9371d4143e24'>gnu: libusb4java: Adjust for building with libusb 1.0.22.</a><span class='msg-avail'>...</span></td><td>Ricardo Wurmus</td></tr>
<tr><td><span title='2018-03-25 20:01:14 +0200'>2018-03-25</span></td><td><a href='/guix/commit/gnu/packages/libusb.scm?id=a667d20e9a7a7ca9d9b9d96efacb4da406439937'>gnu: libmtp: Update to 1.1.15.</a><span class='msg-avail'>...</span></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2018-03-25 20:01:14 +0200'>2018-03-25</span></td><td><a href='/guix/commit/gnu/packages/libusb.scm?id=58ee8a94a90eb40496b9704d541b5dfbbf1685ba'>gnu: libusb: Update to 1.0.22.</a><span class='msg-avail'>...</span></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2018-03-14 17:37:20 +0100'>2018-03-14</span></td><td><a href='/guix/commit/gnu/packages/libusb.scm?id=8c72ed923d77ee55989965bb02628043799b9548'>Merge branch 'master' into core-updates</a></td><td>Ricardo Wurmus</td></tr>
<tr><td><span title='2018-03-13 20:17:11 +0200'>2018-03-13</span></td><td><a href='/guix/commit/gnu/packages/libusb.scm?id=8cf57bc1c6a938fd62deb0e4bf9ef5e460c24669'>gnu: libusb4java: Declare a source file-name.</a><span class='msg-avail'>...</span></td><td>Efraim Flashner</td></tr>
<tr><td><span title='2018-03-11 22:04:40 +0100'>2018-03-11</span></td><td><a href='/guix/commit/gnu/packages/libusb.scm?id=189be331acfda1c242a9c85fca8d2a0356742f48'>build-system/gnu: Add 'bootstrap' phase.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2018-02-11 10:20:41 -0500'>2018-02-11</span></td><td><a href='/guix/commit/gnu/packages/libusb.scm?id=f62dcba42d9812199f6805a95100f8d39c739fde'>gnu: gmtp: Update to 1.3.11.</a><span class='msg-avail'>...</span></td><td>Kei Kebreau</td></tr>
<tr><td><span title='2018-01-10 23:40:35 +0100'>2018-01-10</span></td><td><a href='/guix/commit/gnu/packages/libusb.scm?id=721bdea50bd5d65b7a1be12f369d5dc6ab65b6b8'>gnu: libmtp: Update to 1.1.14.</a><span class='msg-avail'>...</span></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2017-12-28 08:35:24 +0100'>2017-12-28</span></td><td><a href='/guix/commit/gnu/packages/libusb.scm?id=93e5c93e4c3ba60bfe277658b9656e2d9eb2d486'>gnu: Add python-hidapi.</a><span class='msg-avail'>...</span></td><td>Danny Milosavljevic</td></tr>
<tr><td><span title='2017-11-12 03:25:49 +0100'>2017-11-12</span></td><td><a href='/guix/commit/gnu/packages/libusb.scm?id=07cc9245e6def0060fd1b328c09f2637b4381530'>gnu: libusb-compat: Use the same home page as libusb.</a><span class='msg-avail'>...</span></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2017-10-03 17:07:54 +0200'>2017-10-03</span></td><td><a href='/guix/commit/gnu/packages/libusb.scm?id=d109b1e85c5c1438e66dfc05ea4a018418edaf19'>Update e-mail for Theodoros Foradis.</a><span class='msg-avail'>...</span></td><td>Theodoros Foradis</td></tr>
<tr><td><span title='2017-09-04 00:10:59 -0400'>2017-09-04</span></td><td><a href='/guix/commit/gnu/packages/libusb.scm?id=d10092b849153dc27cfed0a9601fde6c7bdec918'>gnu: Put autoconf-related phases immediately after the 'unpack phase.</a><span class='msg-avail'>...</span></td><td>Kei Kebreau</td></tr>
<tr><td><span title='2017-07-20 00:54:52 +0200'>2017-07-20</span></td><td><a href='/guix/commit/gnu/packages/libusb.scm?id=05c88516955814ac61dc7578017e1976c43a1cd3'>gnu: Add libusb@0.1.</a><span class='msg-avail'>...</span></td><td>Jonathan Brielmaier</td></tr>
<tr><td><span title='2017-05-15 22:33:13 +0200'>2017-05-15</span></td><td><a href='/guix/commit/gnu/packages/libusb.scm?id=423b6840b3d7ada3b3c5fef7fdb64b8bbc1acb2b'>gnu: Add java-usb4java.</a><span class='msg-avail'>...</span></td><td>Ricardo Wurmus</td></tr>
<tr><td><span title='2017-05-15 22:33:13 +0200'>2017-05-15</span></td><td><a href='/guix/commit/gnu/packages/libusb.scm?id=18fe5ef1520ee085bf409ee983ed12baf20ea40e'>gnu: Add libusb4java.</a><span class='msg-avail'>...</span></td><td>Ricardo Wurmus</td></tr>
<tr><td><span title='2017-04-06 15:03:07 +0200'>2017-04-06</span></td><td><a href='/guix/commit/gnu/packages/libusb.scm?id=2c273a82f36260cbc68ce65b9f73e581eb471690'>gnu: libusb: Update to 1.0.21.</a><span class='msg-avail'>...</span></td><td>Marius Bakke</td></tr>
<tr><td><span title='2017-04-06 14:58:05 +0200'>2017-04-06</span></td><td><a href='/guix/commit/gnu/packages/libusb.scm?id=05b662663d49883aa5b434c0ce94555ced70fed8'>gnu: libmtp: Update to 1.1.13 [security fixes].</a><span class='msg-avail'>...</span></td><td>Marius Bakke</td></tr>