mips: fix search path for multilib o32

[wzssyqa]

Summary

In the situation of multilib, the gcc objects are in a /32 directory.
On Debian, the libraries is under /libo32 to avoid confliction.

This patch enables clang find gcc in /32, and C lib in /libo32.

[atanasyan]

• Does this problem exist on all versions of Debian or starting from specific version only?
• This fix needs test cases. Take a look at "Check linker invocation on Debian 6 MIPS 32/64-bit" in the clang/test/Driver/linux-ld.c for example.

[wzssyqa]

In D112158#3077049, @atanasyan wrote:

• Does this problem exist on all versions of Debian or starting from specific version only?

This feature starts from llvm-8. And this problem is since then.

• This fix needs test cases. Take a look at "Check linker invocation on Debian 6 MIPS 32/64-bit" in the clang/test/Driver/linux-ld.c for example.

I will do so.

[atanasyan]

LGTM

clang/lib/Driver/ToolChains/Gnu.cpp

MultilibSet DebianMipsMultilibs;
 
     Multilib M64 = Multilib()
                        .gccSuffix("/64")
                        .includeSuffix("/64")
                        .flag("+m64")
                        .flag("-m32")
                        .flag("-mabi=n32");
 
-    Multilib M32 = Multilib().flag("-m64").flag("+m32").flag("-mabi=n32");
+    Multilib M32 =
+        Multilib().gccSuffix("/32").flag("-m64").flag("+m32").flag("-mabi=n32");
 
     DebianMipsMultilibs =
         MultilibSet().Either(M32, M64, MAbiN32).FilterOut(NonExistent);
   }
 
   // Sort candidates. Toolchain that best meets the directories tree goes first.
   // Then select the first toolchains matches command line flags.
   MultilibSet *Candidates[] = {&CSMipsMultilibs, &DebianMipsMultilibs};
static const char *const X86Triples[] = {
       "i386-redhat-linux6E", "i686-redhat-linux",     "i386-redhat-linux",
       "i586-suse-linux",     "i686-montavista-linux", "i686-gnu",
   };
 
   static const char *const M68kLibDirs[] = {"/lib"};
   static const char *const M68kTriples[] = {
       "m68k-linux-gnu", "m68k-unknown-linux-gnu", "m68k-suse-linux"};
 
-  static const char *const MIPSLibDirs[] = {"/lib"};
+  static const char *const MIPSLibDirs[] = {"/libo32", "/lib"};
   static const char *const MIPSTriples[] = {
       "mips-linux-gnu", "mips-mti-linux", "mips-mti-linux-gnu",
       "mips-img-linux-gnu", "mipsisa32r6-linux-gnu"};
-  static const char *const MIPSELLibDirs[] = {"/lib"};
+  static const char *const MIPSELLibDirs[] = {"/libo32", "/lib"};
   static const char *const MIPSELTriples[] = {
       "mipsel-linux-gnu", "mips-img-linux-gnu", "mipsisa32r6el-linux-gnu"};
 
   static const char *const MIPS64LibDirs[] = {"/lib64", "/lib"};
   static const char *const MIPS64Triples[] = {
       "mips64-linux-gnu",      "mips-mti-linux-gnu",
       "mips-img-linux-gnu",    "mips64-linux-gnuabi64",
       "mipsisa64r6-linux-gnu", "mipsisa64r6-linux-gnuabi64"};

clang/lib/Driver/ToolChains/Linux.cpp

#endif
   // This was determined by running GCC in a fake filesystem, creating all
   // possible permutations of these directories, and seeing which ones it added
   // to the link paths.
   path_list &Paths = getFilePaths();
 
   const std::string OSLibDir = std::string(getOSLibDir(Triple, Args));
   const std::string MultiarchTriple = getMultiarchTriple(D, Triple, SysRoot);
 
+  // mips32: Debian multilib, we use /libo32, while in other case, /lib is
+  // used. We need add both libo32 and /lib.
+  if (Arch == llvm::Triple::mips || Arch == llvm::Triple::mipsel)
+    Generic_GCC::AddMultilibPaths(D, SysRoot, "libo32", MultiarchTriple, Paths);
   Generic_GCC::AddMultilibPaths(D, SysRoot, OSLibDir, MultiarchTriple, Paths);
 
   addPathIfExists(D, SysRoot + "/lib/" + MultiarchTriple, Paths);
   addPathIfExists(D, SysRoot + "/lib/../" + OSLibDir, Paths);
 
   if (IsAndroid) {
     // Android sysroots contain a library directory for each supported OS
     // version as well as some unversioned libraries in the usual multiarch