[mips] Fix handling of GNUABIN32 environment in a target triple

The `GNUABIN32` environment in a target triple implies using the N32
ABI. This patch adds support for this environment and switches on N32
ABI if necessary.

Patch by Patch by YunQiang Su.

Differential revision: https://reviews.llvm.org/D51464

llvm-svn: 344570
diff --git a/clang/lib/Driver/ToolChains/Gnu.cpp b/clang/lib/Driver/ToolChains/Gnu.cpp
index cb9e927..b8b69e7 100644
--- a/clang/lib/Driver/ToolChains/Gnu.cpp
+++ b/clang/lib/Driver/ToolChains/Gnu.cpp
@@ -264,11 +264,13 @@
   case llvm::Triple::mipsel:
     return "elf32ltsmip";
   case llvm::Triple::mips64:
-    if (tools::mips::hasMipsAbiArg(Args, "n32"))
+    if (tools::mips::hasMipsAbiArg(Args, "n32") ||
+        T.getEnvironment() == llvm::Triple::GNUABIN32)
       return "elf32btsmipn32";
     return "elf64btsmip";
   case llvm::Triple::mips64el:
-    if (tools::mips::hasMipsAbiArg(Args, "n32"))
+    if (tools::mips::hasMipsAbiArg(Args, "n32") ||
+        T.getEnvironment() == llvm::Triple::GNUABIN32)
       return "elf32ltsmipn32";
     return "elf64ltsmip";
   case llvm::Triple::systemz:
@@ -1855,6 +1857,10 @@
       "mips64el-linux-gnu", "mips-mti-linux-gnu", "mips-img-linux-gnu",
       "mips64el-linux-gnuabi64"};
 
+  static const char *const MIPSN32LibDirs[] = {"/lib32"};
+  static const char *const MIPSN32Triples[] = {"mips64-linux-gnuabin32"};
+  static const char *const MIPSN32ELLibDirs[] = {"/lib32"};
+  static const char *const MIPSN32ELTriples[] = {"mips64el-linux-gnuabin32"};
 
   static const char *const PPCLibDirs[] = {"/lib32", "/lib"};
   static const char *const PPCTriples[] = {
@@ -2051,6 +2057,8 @@
     TripleAliases.append(begin(MIPSTriples), end(MIPSTriples));
     BiarchLibDirs.append(begin(MIPS64LibDirs), end(MIPS64LibDirs));
     BiarchTripleAliases.append(begin(MIPS64Triples), end(MIPS64Triples));
+    BiarchLibDirs.append(begin(MIPSN32LibDirs), end(MIPSN32LibDirs));
+    BiarchTripleAliases.append(begin(MIPSN32Triples), end(MIPSN32Triples));
     break;
   case llvm::Triple::mipsel:
     LibDirs.append(begin(MIPSELLibDirs), end(MIPSELLibDirs));
@@ -2058,18 +2066,24 @@
     TripleAliases.append(begin(MIPSTriples), end(MIPSTriples));
     BiarchLibDirs.append(begin(MIPS64ELLibDirs), end(MIPS64ELLibDirs));
     BiarchTripleAliases.append(begin(MIPS64ELTriples), end(MIPS64ELTriples));
+    BiarchLibDirs.append(begin(MIPSN32ELLibDirs), end(MIPSN32ELLibDirs));
+    BiarchTripleAliases.append(begin(MIPSN32ELTriples), end(MIPSN32ELTriples));
     break;
   case llvm::Triple::mips64:
     LibDirs.append(begin(MIPS64LibDirs), end(MIPS64LibDirs));
     TripleAliases.append(begin(MIPS64Triples), end(MIPS64Triples));
     BiarchLibDirs.append(begin(MIPSLibDirs), end(MIPSLibDirs));
     BiarchTripleAliases.append(begin(MIPSTriples), end(MIPSTriples));
+    BiarchLibDirs.append(begin(MIPSN32LibDirs), end(MIPSN32LibDirs));
+    BiarchTripleAliases.append(begin(MIPSN32Triples), end(MIPSN32Triples));
     break;
   case llvm::Triple::mips64el:
     LibDirs.append(begin(MIPS64ELLibDirs), end(MIPS64ELLibDirs));
     TripleAliases.append(begin(MIPS64ELTriples), end(MIPS64ELTriples));
     BiarchLibDirs.append(begin(MIPSELLibDirs), end(MIPSELLibDirs));
     BiarchTripleAliases.append(begin(MIPSELTriples), end(MIPSELTriples));
+    BiarchLibDirs.append(begin(MIPSN32ELLibDirs), end(MIPSN32ELLibDirs));
+    BiarchTripleAliases.append(begin(MIPSN32ELTriples), end(MIPSN32ELTriples));
     BiarchTripleAliases.append(begin(MIPSTriples), end(MIPSTriples));
     break;
   case llvm::Triple::ppc: