Add -fplugin=name.so option to the driver

This translates to -load name.so in the cc1 command. We can't name the driver
option -load, as that means "link against oad", so instead we follow GCC's lead
and name the option -fplugin.

llvm-svn: 248378
diff --git a/clang/lib/Driver/Tools.cpp b/clang/lib/Driver/Tools.cpp
index f407021..7354421 100644
--- a/clang/lib/Driver/Tools.cpp
+++ b/clang/lib/Driver/Tools.cpp
@@ -5037,6 +5037,13 @@
   // Forward -fparse-all-comments to -cc1.
   Args.AddAllArgs(CmdArgs, options::OPT_fparse_all_comments);
 
+  // Turn -fplugin=name.so into -load name.so
+  for (const Arg *A : Args.filtered(options::OPT_fplugin_EQ)) {
+    CmdArgs.push_back("-load");
+    CmdArgs.push_back(A->getValue());
+    A->claim();
+  }
+
   // Forward -Xclang arguments to -cc1, and -mllvm arguments to the LLVM option
   // parser.
   Args.AddAllArgValues(CmdArgs, options::OPT_Xclang);