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/lib/Driver/Distro.cpp b/lib/Driver/Distro.cpp
index ee4fe841..f0313bbe 100644
--- a/lib/Driver/Distro.cpp
+++ b/lib/Driver/Distro.cpp
@@ -93,6 +93,10 @@ 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/lib/Driver/ToolChains/Cuda.cpp b/lib/Driver/ToolChains/Cuda.cpp
index d14776c5..88bc3ccd 100644
--- a/lib/Driver/ToolChains/Cuda.cpp
+++ b/lib/Driver/ToolChains/Cuda.cpp
@@ -119,6 +119,9 @@ 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/lib/Driver/ToolChains/Linux.cpp b/lib/Driver/ToolChains/Linux.cpp
--- a/lib/Driver/ToolChains/Linux.cpp
+++ b/lib/Driver/ToolChains/Linux.cpp
@@ -186,6 +186,10 @@
 
   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()) {
@@ -251,6 +255,7 @@
 
   if (IsAndroid || Distro.IsOpenSUSE())
     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.
@@ -264,6 +269,7 @@
 
   Generic_GCC::AddMultilibPaths(D, SysRoot, OSLibDir, MultiarchTriple, Paths);
 
+#if 0
   addPathIfExists(D, SysRoot + "/lib/" + MultiarchTriple, Paths);
   addPathIfExists(D, SysRoot + "/lib/../" + OSLibDir, Paths);
 
@@ -295,9 +301,11 @@
     addPathIfExists(D, SysRoot + "/" + OSLibDir + "/" + ABIName, Paths);
     addPathIfExists(D, SysRoot + "/usr/" + OSLibDir + "/" + ABIName, Paths);
   }
+#endif
 
   Generic_GCC::AddMultiarchPaths(D, SysRoot, OSLibDir, Paths);
 
+#if 0
   // Similar to the logic for GCC above, if we are currently running Clang
   // inside of the requested system root, add its parent library path to those
   // searched.
@@ -305,9 +313,14 @@
   // directory ('Dir' below) or the ResourceDir.
   if (StringRef(D.Dir).startswith(SysRoot))
     addPathIfExists(D, D.Dir + "/../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);
 
-  addPathIfExists(D, SysRoot + "/lib", Paths);
-  addPathIfExists(D, SysRoot + "/usr/lib", Paths);
+  // Add GCC's lib/ directory so libstdc++.so can be found.
+  addPathIfExists(D, GCCInstallation.getParentLibPath(), Paths);
 }
 
 ToolChain::RuntimeLibType Linux::GetDefaultRuntimeLibType() const {
ewise.
* gnu/packages/ibus.scm (ibus-rime)[native-inputs]: Likewise.
* gnu/packages/rust.scm (rust-1.19)[native-inputs]: Likewise.
* gnu/packages/simulation.scm (fenics)[native-inputs]: Likewise.
* gnu/packages/squirrel.scm (squirrel)[native-inputs]: Likewise.
* gnu/packages/video.scm (handbrake)[native-inputs]: Likewise.
* gnu/packages/virtualization.scm (xen)[native-inputs]: Likewise.
* gnu/packages/vulkan.scm (shaderc)[native-inputs]: Likewise.
</span></span></td><td>Marius Bakke</td></tr>
<tr><td><span title='2019-05-25 06:08:23 -0400'>2019-05-25</span></td><td><a href='/guix/commit/gnu/packages/squirrel.scm?id=41cdaf47e1a398f91a1a06648ebb2a997cfdf224'>gnu: squirrel: Fix build.</a><span class='msg-avail'>...<span class='msg-tooltip'>This follows commit 9d0c291e3e.

* gnu/packages/squirrel.scm: Adjust module reference.
</span></span></td><td>Kei Kebreau</td></tr>
<tr><td><span title='2019-05-24 21:00:15 -0400'>2019-05-24</span></td><td><a href='/guix/commit/gnu/packages/squirrel.scm?id=608d148c50962bc217b6481f60507873801464cf'>gnu: squirrel: Install headers and documentation.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/squirrel.scm (squirrel)[arguments]: Disable building static
libraries. Add 'install-documentation' and 'install-headers' phases.
[native-inputs]: Add python-sphinx.
</span></span></td><td>Kei Kebreau</td></tr>
<tr><td><span title='2019-05-24 21:00:15 -0400'>2019-05-24</span></td><td><a href='/guix/commit/gnu/packages/squirrel.scm?id=03b630686fe96793e87f1323330d3c724abd2e14'>gnu: squirrel: Build from a source archive instead of a Git checkout.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/squirrel.scm (squirrel)[source]: Use url-fetch and adjust the
source URL accordingly.
</span></span></td><td>Kei Kebreau</td></tr>
<tr><td><span title='2019-05-22 21:36:45 -0400'>2019-05-22</span></td><td><a href='/guix/commit/gnu/packages/squirrel.scm?id=39d655f8cf1448fa28c6157e02c7a41eb23ca66a'>gnu: Add squirrel.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/squirrel.scm: New file.
* gnu/local.mk (GNU_SYSTEM_MODULES): Add it.
</span></span></td><td>Andy Tai</td></tr>