For Linux/gnu compatibility, preinclude <stdc-predef.h> if the file is available

As reported in llvm bugzilla 32377.
Here’s a patch to add preinclude of stdc-predef.h.

The gcc documentation says “On GNU/Linux, <stdc-predef.h> is pre-included.” 
See https://gcc.gnu.org/gcc-4.8/porting_to.html;

The preinclude is inhibited with –ffreestanding.

Basically I fixed the failing test cases by adding –ffreestanding which inhibits
this behavior.

I fixed all the failing tests, including some in extra/test, there's a separate
patch for that which is linked here

Patch By: mibintc

Differential Revision: https://reviews.llvm.org/D34158

llvm-svn: 318669

1 files changed, 13 insertions, 0 deletions

diff --git a/clang/lib/Driver/ToolChains/Linux.cpp b/clang/lib/Driver/ToolChains/Linux.cpp
index ca042f38db8..5ae250759b1 100644
--- a/clang/lib/Driver/ToolChains/Linux.cpp
+++ b/clang/lib/Driver/ToolChains/Linux.cpp
@@ -710,6 +710,8 @@ void Linux::AddClangSystemIncludeArgs(const ArgList &DriverArgs,
   addExternCSystemInclude(DriverArgs, CC1Args, SysRoot + "/include");
 
   addExternCSystemInclude(DriverArgs, CC1Args, SysRoot + "/usr/include");
+
+  AddGnuIncludeArgs(DriverArgs, CC1Args);
 }
 
 static std::string DetectLibcxxIncludePath(StringRef base) {
@@ -748,6 +750,17 @@ std::string Linux::findLibCxxIncludePath() const {
   return "";
 }
 
+void Linux::AddGnuIncludeArgs(const llvm::opt::ArgList &DriverArgs,
+                              llvm::opt::ArgStringList &CC1Args) const {
+  if (!DriverArgs.hasArg(options::OPT_ffreestanding)) {
+    // For gcc compatibility, clang will preinclude <stdc-predef.h>
+    // -ffreestanding suppresses this behavior.
+    CC1Args.push_back("-fsystem-include-if-exists");
+    CC1Args.push_back("stdc-predef.h");
+  }
+}
+
+
 void Linux::addLibStdCxxIncludePaths(const llvm::opt::ArgList &DriverArgs,
                                      llvm::opt::ArgStringList &CC1Args) const {
   // We need a detected GCC installation on Linux to provide libstdc++'s