Clang attempts to guess file names based on the OS and distro (yes!),
but unfortunately, that doesn't work for us.

This patch makes it easy to insert libc's $libdir so that Clang passes the
correct absolute file name of crt1.o etc. to 'ld'.  It also disables all
the distro-specific stuff and removes the hard-coded FHS directory names
to make sure Clang also works on non-GuixSD systems.

This patch makes slight adjustments over "clang-libc-search-path.patch" for
changes in clang 3.8.

--- cfe-3.8.0.src/lib/Driver/ToolChains.cpp
+++ cfe-3.8.0.src/lib/Driver/ToolChains.cpp
@@ -3661,6 +3661,9 @@
                          GCCInstallation.getTriple().str() + "/bin")
                        .str());
 
+  // Comment out the distro-specific tweaks so that they don't bite when
+  // using Guix on a foreign distro.
+#if 0
   Distro Distro = DetectDistro(D, Arch);
 
   if (IsOpenSUSE(Distro) || IsUbuntu(Distro)) {
@@ -3702,6 +3705,7 @@
 
   if (IsOpenSUSE(Distro))
     ExtraOpts.push_back("--enable-new-dtags");
+#endif
 
   // The selection of paths to try here is designed to match the patterns which
   // the GCC driver itself uses, as this is part of the GCC-compatible driver.
@@ -3771,14 +3775,12 @@
     addPathIfExists(D, D.Dir + "/../" + OSLibDir, Paths);
   }
 
-  addPathIfExists(D, SysRoot + "/lib/" + MultiarchTriple, Paths);
-  addPathIfExists(D, SysRoot + "/lib/../" + OSLibDir, Paths);
-  addPathIfExists(D, SysRoot + "/usr/lib/" + MultiarchTriple, Paths);
-  addPathIfExists(D, SysRoot + "/usr/lib/../" + OSLibDir, Paths);
-
   // Try walking via the GCC triple path in case of biarch or multiarch GCC
   // installations with strange symlinks.
   if (GCCInstallation.isValid()) {
+    // The following code would end up adding things like
+    // "/usr/lib/x86_64-unknown-linux-gnu/../../lib64" to the search path.
+#if 0
     addPathIfExists(D,
                     SysRoot + "/usr/lib/" + GCCInstallation.getTriple().str() +
                         "/../../" + OSLibDir,
@@ -3791,6 +3793,7 @@
                              BiarchSibling.gccSuffix(),
                       Paths);
     }
+#endif
 
     // See comments above on the multilib variant for details of why this is
     // included even from outside the sysroot.
@@ -3815,8 +3818,9 @@
   if (StringRef(D.Dir).startswith(SysRoot))
     addPathIfExists(D, D.Dir + "/../lib", Paths);
 
-  addPathIfExists(D, SysRoot + "/lib", Paths);
-  addPathIfExists(D, SysRoot + "/usr/lib", Paths);
+  // Add libc's lib/ directory to the search path, so that crt1.o, crti.o,
+  // and friends can be found.
+  addPathIfExists(D, "@GLIBC_LIBDIR@", Paths);
 }
 
 bool Linux::HasNativeLLVMSupport() const { return true; }
e783087ad8b9b4289d0ef581a5a'>Thank Thomas.</a></td><td>Ricardo Wurmus</td></tr>
<tr><td><span title='2015-11-23 17:48:35 +0100'>2015-11-23</span></td><td><a href='/guix/commit/THANKS?id=160b0ef3fd87c73b140f4480a521ad8c80475ab3'>Thank Jan.</a></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2015-11-17 09:44:52 +0100'>2015-11-17</span></td><td><a href='/guix/commit/THANKS?id=87450b12744bf1f508b6fd4ee11c00af35fcc4ee'>Thank Chris.</a></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2015-10-09 20:57:24 +0200'>2015-10-09</span></td><td><a href='/guix/commit/THANKS?id=28eb956dfeb8b759e690cf3e30dfe85788561778'>Thank Chris.</a></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2015-09-20 22:06:48 +0200'>2015-09-20</span></td><td><a href='/guix/commit/THANKS?id=8fcac19975b163e0e5b98d27a52cb7c541bf94d9'>Thank Petter.</a></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2015-08-27 23:34:23 +0200'>2015-08-27</span></td><td><a href='/guix/commit/THANKS?id=25ae74cffaa95cc4e509e3363f6f6525ddc21672'>Thank Eric Hanchrow.</a></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2015-07-23 09:42:24 +0200'>2015-07-23</span></td><td><a href='/guix/commit/THANKS?id=015878fdbbfe5e30474bea229c014677e04cc27f'>Thank Anders.</a></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2015-07-22 23:47:35 +0200'>2015-07-22</span></td><td><a href='/guix/commit/THANKS?id=0e9f9f7bc23a7e7f2390eb1bbb09f36f33cda534'>Thank Malcolm.</a></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2015-07-22 22:56:42 +0200'>2015-07-22</span></td><td><a href='/guix/commit/THANKS?id=31ea3ebb0570c070df578d5983bdcdce117e4376'>Thank Dave.</a></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2015-07-04 12:13:01 +0300'>2015-07-04</span></td><td><a href='/guix/commit/THANKS?id=e7c48ee9519aa5cd094f3326a4caeccba072e9fd'>Clean up 'THANKS' and 'AUTHORS'.</a><span class='msg-avail'>...<span class='msg-tooltip'>* THANKS: Add Konrad Hinsen, Cyprien Nicolas, Yakkala Yagnesh Raghava
  and Alexander Shendi.  Remove Federico Beffa, Marek Benc, John
  Darrington, rekado, Cyrill Schenkel and Andy Wingo because they are
  placed in AUTHORS.  Move Amirouche Boubekki and Alex Kost to ...
* AUTHORS: ... here.  Add Arne Babenhauserheide, Ian Denhardt, Kevin
  Lemonnier, Mathieu Lirzin, Pierre-Antoine Rault and Ben Woodcroft.
  Fix some names and emails.
</span></span></td><td>Alex Kost</td></tr>
<tr><td><span title='2015-06-07 18:15:40 +0200'>2015-06-07</span></td><td><a href='/guix/commit/THANKS?id=a647e0b8eef9931a46aded4c4d71e0413cc84340'>Thank Thomas.</a></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2015-05-01 00:06:18 +0200'>2015-05-01</span></td><td><a href='/guix/commit/THANKS?id=0aaca4354c68a21b01ce5fcd7fb7f820e58fc3cb'>Thank Joshua.</a></td><td>Ludovic Courtès</td></tr>