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 foreign distros.

diff --git a/clang/lib/Driver/Distro.cpp b/clang/lib/Driver/Distro.cpp
index a7e7f169dc14..0564003352a4 100644
--- a/clang/lib/Driver/Distro.cpp
+++ b/clang/lib/Driver/Distro.cpp
@@ -100,6 +100,10 @@ static Distro::DistroType DetectLsbRelease(llvm::vfs::FileSystem &VFS) {
 }
 
 static Distro::DistroType DetectDistro(llvm::vfs::FileSystem &VFS) {
+  // The compiler should always behave the same, even when used via Guix on a
+  // foreign distro.
+  return Distro::UnknownDistro;
+
   Distro::DistroType Version = Distro::UnknownDistro;
 
   // Newer freedesktop.org's compilant systemd-based systems
diff --git a/clang/lib/Driver/ToolChains/Cuda.cpp b/clang/lib/Driver/ToolChains/Cuda.cpp
index 1462576ca870..1078dba8f481 100644
--- a/clang/lib/Driver/ToolChains/Cuda.cpp
+++ b/clang/lib/Driver/ToolChains/Cuda.cpp
@@ -132,6 +132,9 @@ CudaInstallationDetector::CudaInstallationDetector(
     const Driver &D, const llvm::Triple &HostTriple,
     const llvm::opt::ArgList &Args)
     : D(D) {
+  // Don't look for CUDA in /usr.
+  return;
+
   struct Candidate {
     std::string Path;
     bool StrictChecking;
diff --git a/clang/lib/Driver/ToolChains/Linux.cpp b/clang/lib/Driver/ToolChains/Linux.cpp
index 4300a2bdff17..ac3b29d0fc13 100644
--- a/clang/lib/Driver/ToolChains/Linux.cpp
+++ b/clang/lib/Driver/ToolChains/Linux.cpp
@@ -224,6 +224,10 @@ Linux::Linux(const Driver &D, const llvm::Triple &Triple, const ArgList &Args)
 
   Generic_GCC::PushPPaths(PPaths);
 
+  // Comment out the distro-specific tweaks so that they don't bite when
+  // using Guix on a foreign distro.
+#if 0
+
   Distro Distro(D.getVFS(), Triple);
 
   if (Distro.IsAlpineLinux() || Triple.isAndroid()) {
@@ -284,6 +288,7 @@ Linux::Linux(const Driver &D, const llvm::Triple &Triple, const ArgList &Args)
 
 #ifdef ENABLE_LINKER_BUILD_ID
   ExtraOpts.push_back("--build-id");
+#endif
 #endif
 
   // The selection of paths to try here is designed to match the patterns which
@@ -305,6 +310,7 @@ Linux::Linux(const Driver &D, const llvm::Triple &Triple, const ArgList &Args)
   }
   Generic_GCC::AddMultilibPaths(D, SysRoot, OSLibDir, MultiarchTriple, Paths);
 
+#if 0
   addPathIfExists(D, concat(SysRoot, "/lib", MultiarchTriple), Paths);
   addPathIfExists(D, concat(SysRoot, "/lib/..", OSLibDir), Paths);
 
@@ -333,11 +339,21 @@ Linux::Linux(const Driver &D, const llvm::Triple &Triple, const ArgList &Args)
     addPathIfExists(D, concat(SysRoot, "/", OSLibDir, ABIName), Paths);
     addPathIfExists(D, concat(SysRoot, "/usr", OSLibDir, ABIName), Paths);
   }
+#endif
 
   Generic_GCC::AddMultiarchPaths(D, SysRoot, OSLibDir, Paths);
 
+#if 0
   addPathIfExists(D, concat(SysRoot, "/lib"), Paths);
   addPathIfExists(D, concat(SysRoot, "/usr/lib"), Paths);
+#endif
+
+  // 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);
+
+  // Add GCC's lib/ directory so libstdc++.so can be found.
+  addPathIfExists(D, GCCInstallation.getParentLibPath(), Paths);
 }
 
 ToolChain::RuntimeLibType Linux::GetDefaultRuntimeLibType() const {
d74e2713'>import: crate: Trim version for names after left-most non-zero part.</a><span class='msg-avail'>...</span></td><td>Hartmut Goebel</td></tr>
<tr><td><span title='2020-12-02 22:09:23 +0100'>2020-12-02</span></td><td><a href='/guix/commit/tests/crate.scm?id=9a48e35be853e10ba9b21bb91ef52a66b4264c84'>import: utils: Trim patch version from names.</a><span class='msg-avail'>...</span></td><td>Hartmut Goebel</td></tr>
<tr><td><span title='2020-12-02 22:09:23 +0100'>2020-12-02</span></td><td><a href='/guix/commit/tests/crate.scm?id=50fbb3f032b46a565ca225daddf4eeb7c8edfab4'>import: crate: Parameterized importing of dev dependencies.</a><span class='msg-avail'>...</span></td><td>Martin Becze</td></tr>
<tr><td><span title='2020-12-02 22:09:23 +0100'>2020-12-02</span></td><td><a href='/guix/commit/tests/crate.scm?id=269c1db41bd82f93c7ae5c62a4969a423e556183'>import: crate: Use guile-semver to resolve module versions.</a><span class='msg-avail'>...</span></td><td>Martin Becze</td></tr>
<tr><td><span title='2020-04-27 23:29:40 +0200'>2020-04-27</span></td><td><a href='/guix/commit/tests/crate.scm?id=5dfe02c60767a633c67f7f6fc9557b54b3c99b63'>tests: Remove trailing commas in JSON tests.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>