[clang] Add gcc-toolset-10 support (RHEL/CentOS 8)

[simoll]

Summary

Clang only adds GCC paths for RHEL <= 7 'devtoolset-<N>' Software Collections (SCL). This generalizes this support to also include the 'gcc-toolset-10' SCL in RHEL/CentOS 8.

[stephan.dollberg]

LGTM but probably want to apply clang-format suggestion.

clang/lib/Driver/ToolChains/Gnu.cpp

2055

Comment only says CentOS while title also says RHEL. I assume it applies to both?

Might also want to merge with the comment below as they are kind of the same thing.

clang/lib/Driver/ToolChains/Gnu.cpp

for (llvm::vfs::directory_iterator LI = D.getVFS().dir_begin(PrefixDir, EC),
 
       Prefixes.push_back(CandidatePrefix);
     }
     return;
   }
 
   // Non-Solaris is much simpler - most systems just go with "/usr".
   if (SysRoot.empty() && TargetTriple.getOS() == llvm::Triple::Linux) {
-    // Yet, still look for RHEL devtoolsets.
+    // Yet, still look for RHEL/CentOS devtoolsets and gcc-toolsets.
+    Prefixes.push_back("/opt/rh/gcc-toolset-10/root/usr");
     Prefixes.push_back("/opt/rh/devtoolset-10/root/usr");
     Prefixes.push_back("/opt/rh/devtoolset-9/root/usr");
     Prefixes.push_back("/opt/rh/devtoolset-8/root/usr");
     Prefixes.push_back("/opt/rh/devtoolset-7/root/usr");
     Prefixes.push_back("/opt/rh/devtoolset-6/root/usr");
     Prefixes.push_back("/opt/rh/devtoolset-4/root/usr");
     Prefixes.push_back("/opt/rh/devtoolset-3/root/usr");
     Prefixes.push_back("/opt/rh/devtoolset-2/root/usr");

clang/lib/Driver/ToolChains/Linux.cpp

Linux::Linux(const Driver &D, const llvm::Triple &Triple, const ArgList &Args)
 
   // Android ARM/AArch64 use max-page-size=4096 to reduce VMA usage. Note, lld
   // from 11 onwards default max-page-size to 65536 for both ARM and AArch64.
   if ((Triple.isARM() || Triple.isAArch64()) && Triple.isAndroid()) {
     ExtraOpts.push_back("-z");
     ExtraOpts.push_back("max-page-size=4096");
   }
 
-  if (GCCInstallation.getParentLibPath().find("opt/rh/devtoolset") !=
-      StringRef::npos)
+  if (GCCInstallation.getParentLibPath().find("opt/rh/") != StringRef::npos)
     // With devtoolset on RHEL, we want to add a bin directory that is relative
     // to the detected gcc install, because if we are using devtoolset gcc then
     // we want to use other tools from devtoolset (e.g. ld) instead of the
     // standard system tools.
     PPaths.push_back(Twine(GCCInstallation.getParentLibPath() +
                      "/../bin").str());
 
   if (Arch == llvm::Triple::arm || Arch == llvm::Triple::thumb)