gnu: clang@10: Do not refer to /lib on foreign distros.

Partly fixes <https://issues.guix.gnu.org/51088>.

* gnu/packages/patches/clang-10.0-libc-search-path.patch: Update.

gnu/packages/patches/clang-10.0-libc-search-path.patch

@@ -4,18 +4,47 @@ 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-Guix systems.
+to make sure Clang also works on foreign distros.
 
+diff --git a/lib/Driver/Distro.cpp b/lib/Driver/Distro.cpp
+index 06707fef..f3bd43de 100644
+--- a/lib/Driver/Distro.cpp
++++ b/lib/Driver/Distro.cpp
+@@ -20,6 +20,10 @@ using namespace clang;
+ 
+ static Distro::DistroType DetectDistro(llvm::vfs::FileSystem &VFS,
+                                        const llvm::Triple &TargetOrHost) {
++  // The compiler should always behave the same, even when used via Guix on a
++  // foreign distro.
++  return Distro::UnknownDistro;
++
+   // If we don't target Linux, no need to check the distro. This saves a few
+   // OS calls.
+   if (!TargetOrHost.isOSLinux())
+diff --git a/lib/Driver/ToolChains/Cuda.cpp b/lib/Driver/ToolChains/Cuda.cpp
+index 50d22a2a..4ab93e0a 100644
+--- a/lib/Driver/ToolChains/Cuda.cpp
++++ b/lib/Driver/ToolChains/Cuda.cpp
+@@ -60,6 +60,9 @@ 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
-index bff1ab10..79e1477e 100644
+index bff1ab10..e996d3b8 100644
 --- a/lib/Driver/ToolChains/Linux.cpp
 +++ b/lib/Driver/ToolChains/Linux.cpp
 @@ -240,6 +240,9 @@ Linux::Linux(const Driver &D, const llvm::Triple &Triple, const ArgList &Args)
                           .str());
    }
  
-+// Comment out the distro-specific tweaks so that they don't bite when
++  // Comment out the distro-specific tweaks so that they don't bite when
-+// using Guix on a foreign distro.
++  // using Guix on a foreign distro.
 +#if 0
    Distro Distro(D.getVFS(), Triple);
  
@@ -24,61 +53,41 @@ index bff1ab10..79e1477e 100644
  
    if (IsAndroid || Distro.IsOpenSUSE())
      ExtraOpts.push_back("--enable-new-dtags");
-+#endif	// Guix
++#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.
-@@ -363,7 +367,7 @@ Linux::Linux(const Driver &D, const llvm::Triple &Triple, const ArgList &Args)
+@@ -369,6 +373,7 @@ Linux::Linux(const Driver &D, const llvm::Triple &Triple, const ArgList &Args)
-     // the cross. Note that GCC does include some of these directories in some
-     // configurations but this seems somewhere between questionable and simply
-     // a bug.
--    if (StringRef(LibPath).startswith(SysRoot)) {
-+    if (0) {
-       addPathIfExists(D, LibPath + "/" + MultiarchTriple, Paths);
-       addPathIfExists(D, LibPath + "/../" + OSLibDir, Paths);
      }
-@@ -382,6 +386,8 @@ Linux::Linux(const Driver &D, const llvm::Triple &Triple, const ArgList &Args)
-   addPathIfExists(D, SysRoot + "/lib/" + MultiarchTriple, Paths);
-   addPathIfExists(D, SysRoot + "/lib/../" + OSLibDir, Paths);
- 
-+// This requires the commented distro tweaks above.
-+#if 0
-   if (IsAndroid) {
-     // Android sysroots contain a library directory for each supported OS
-     // version as well as some unversioned libraries in the usual multiarch
-@@ -410,10 +416,15 @@ Linux::Linux(const Driver &D, const llvm::Triple &Triple, const ArgList &Args)
-     addPathIfExists(D, SysRoot + "/" + OSLibDir + "/" + ABIName, Paths);
-     addPathIfExists(D, SysRoot + "/usr/" + OSLibDir + "/" + ABIName, Paths);
    }
-+#endif
  
++#if 0
+   // Similar to the logic for GCC above, if we currently running Clang inside
+   // of the requested system root, add its parent library paths to
+   // those searched.
+@@ -414,6 +419,8 @@ Linux::Linux(const Driver &D, const llvm::Triple &Triple, const ArgList &Args)
    // 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
-+// The following code would end up adding things like
++    // "/usr/lib/x86_64-unknown-linux-gnu/../../lib64" to the search path.
-+// "/usr/lib/x86_64-unknown-linux-gnu/../../lib64" to the search path.
-+#if 0
      addPathIfExists(D,
                      SysRoot + "/usr/lib/" + GCCInstallation.getTriple().str() +
                          "/../../" + OSLibDir,
-@@ -426,6 +437,7 @@ Linux::Linux(const Driver &D, const llvm::Triple &Triple, const ArgList &Args)
+@@ -449,9 +456,14 @@ Linux::Linux(const Driver &D, const llvm::Triple &Triple, const ArgList &Args)
-                              BiarchSibling.gccSuffix(),
+   // directory ('Dir' below) or the ResourceDir.
-                       Paths);
-     }
-+#endif
- 
-     // See comments above on the multilib variant for details of why this is
-     // included even from outside the sysroot.
-@@ -450,8 +462,9 @@ Linux::Linux(const Driver &D, const llvm::Triple &Triple, const ArgList &Args)
    if (StringRef(D.Dir).startswith(SysRoot))
      addPathIfExists(D, D.Dir + "/../lib", Paths);
- 
++#endif
--  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);
+ 
+-  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::CXXStdlibType Linux::GetDefaultCXXStdlibType() const {