Distro: initial support for alpine

[martell]

Summary

Add alpine linux as a distro.
We support building for musl from musl since rL292848.
Let's add this important docker / kubernetes empowering distro.

[martell]

@rnk ping.
Feel free to add anyone you think might be more suitable if you can't review this.

[rnk]

lgtm

[mgorny]

I'm sorry for being late to the party but could you update unittests/Driver/DistroTest.cpp as well?

include/clang/Driver/Distro.h

 /// as well as helper functions that match the specific (versioned) results
 /// into wider distribution classes.
 class Distro {
 public:
   enum DistroType {
     // NB: Releases of a particular Linux distro should be kept together
     // in this enum, because some tests are done by integer comparison against
     // the first and last known member in the family, e.g. IsRedHat().
+    AlpineLinux,
     ArchLinux,
     DebianLenny,
     DebianSqueeze,
     DebianWheezy,
     DebianJessie,
     DebianStretch,
     DebianBuster,
     Exherbo,

lib/Driver/Distro.cpp

for (const StringRef& Line : Lines) {
       return Distro::UnknownDistro;
     }
     return Distro::UnknownDistro;
   }
 
   if (VFS.exists("/etc/exherbo-release"))
     return Distro::Exherbo;
 
+  if (VFS.exists("/etc/alpine-release"))
+    return Distro::AlpineLinux;
+
   if (VFS.exists("/etc/arch-release"))
     return Distro::ArchLinux;
 
   return Distro::UnknownDistro;
 }
 
 Distro::Distro(vfs::FileSystem &VFS) : DistroVal(DetectDistro(VFS)) {}

lib/Driver/ToolChains/Linux.cpp

Linux::Linux(const Driver &D, const llvm::Triple &Triple, const ArgList &Args)
   // FIXME: This seems unlikely to be Linux-specific.
   ToolChain::path_list &PPaths = getProgramPaths();
   PPaths.push_back(Twine(GCCInstallation.getParentLibPath() + "/../" +
                          GCCInstallation.getTriple().str() + "/bin")
                        .str());
 
   Distro Distro(D.getVFS());
 
-  if (Distro.IsOpenSUSE() || Distro.IsUbuntu()) {
+  if (Distro.IsAlpineLinux()) {
+    ExtraOpts.push_back("-z");
+    ExtraOpts.push_back("now");
+  }
+
+  if (Distro.IsOpenSUSE() || Distro.IsUbuntu() || Distro.IsAlpineLinux()) {
     ExtraOpts.push_back("-z");
     ExtraOpts.push_back("relro");
   }
 
   if (Arch == llvm::Triple::arm || Arch == llvm::Triple::thumb)
     ExtraOpts.push_back("-X");
 
   const bool IsAndroid = Triple.isAndroid();
   const bool IsMips = tools::isMipsArch(Arch);
   const bool IsHexagon = Arch == llvm::Triple::hexagon;
 
   if (IsMips && !SysRoot.empty())
     ExtraOpts.push_back("--sysroot=" + SysRoot);
 
   // Do not use 'gnu' hash style for Mips targets because .gnu.hash
   // and the MIPS ABI require .dynsym to be sorted in different ways.
   // .gnu.hash needs symbols to be grouped by hash code whereas the MIPS
   // ABI requires a mapping between the GOT and the symbol table.
   // Android loader does not support .gnu.hash.
   // Hexagon linker/loader does not support .gnu.hash
   if (!IsMips && !IsAndroid && !IsHexagon) {
-    if (Distro.IsRedhat() || Distro.IsOpenSUSE() ||
+    if (Distro.IsRedhat() || Distro.IsOpenSUSE() || Distro.IsAlpineLinux() ||
         (Distro.IsUbuntu() && Distro >= Distro::UbuntuMaverick))
       ExtraOpts.push_back("--hash-style=gnu");
 
     if (Distro.IsDebian() || Distro.IsOpenSUSE() || Distro == Distro::UbuntuLucid ||
         Distro == Distro::UbuntuJaunty || Distro == Distro::UbuntuKarmic)
       ExtraOpts.push_back("--hash-style=both");
   }