Make library/header paths visible to cmd/go script tests, which is necessary for
cgo/gccgo tests to work correctly

diff --git a/src/cmd/go/script_test.go b/src/cmd/go/script_test.go
index dfaa40548e..9d0f0e9bcd 100644
--- a/src/cmd/go/script_test.go
+++ b/src/cmd/go/script_test.go
@@ -100,6 +100,10 @@ const (
 var extraEnvKeys = []string{
 	"SYSTEMROOT",         // must be preserved on Windows to find DLLs; golang.org/issue/25210
 	"WINDIR",             // must be preserved on Windows to be able to run PowerShell command; golang.org/issue/30711
+	"CPATH",
+	"C_INCLUDE_PATH",
+	"CPLUS_INCLUDE_PATH",
+	"LIBRARY_PATH",
 	"LD_LIBRARY_PATH",    // must be preserved on Unix systems to find shared libraries
 	"CC",                 // don't lose user settings when invoking cgo
 	"GO_TESTING_GOTOOLS", // for gccgo testing
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<tr><td><span title='2021-05-20 01:58:04 +0200'>2021-05-20</span></td><td><a href='/guix/commit/README?id=c0087d33705f53cc3619a1a43a33602aaecc3a8b'>The #guix channel is hosted by Libera Chat.</a><span class='msg-avail'>...</span></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2020-10-23 12:57:20 -0400'>2020-10-23</span></td><td><a href='/guix/commit/README?id=b5aaa3a4fb985d21e21e2a67f48b52f13ebd4728'>doc: Update README.</a><span class='msg-avail'>...</span></td><td>Maxim Cournoyer</td></tr>
<tr><td><span title='2020-10-22 22:47:54 -0400'>2020-10-22</span></td><td><a href='/guix/commit/README?id=503d2bfde08f9bf97bbf430516d2f19faedd4319'>README: Refer to the manual for building from Git.</a><span class='msg-avail'>...</span></td><td>Maxim Cournoyer</td></tr>
<tr><td><span title='2020-06-02 18:55:53 +0200'>2020-06-02</span></td><td><a href='/guix/commit/README?id=c75a80189fc19f6ff8b4c82d1d1801be6763b6d2'>doc: Update README to refer to the manual.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>