Add a default system include of '/include'. This isn't particularly

useful when using Clang as a system-compiler, but its harmless. When
using Clang as a cross-compiler, this can be very handy as quite a few
toolchains ship their libc headers here rather than under
'/usr/include'.

For reference, this is the beginning of my work to also make the Clang
driver more suitable as a cross-compiler.

llvm-svn: 144089

clang/lib/Driver/ToolChains.cpp

@@ -1987,6 +1987,11 @@ void Linux::AddClangSystemIncludeArgs(const ArgList &DriverArgs,
   if (getTriple().getOS() == llvm::Triple::RTEMS)
     return;
 
+  // Add an include of '/include' directly. This isn't provided by default by
+  // system GCCs, but is often used with cross-compiling GCCs, and harmless to
+  // add even when Clang is acting as-if it were a system compiler.
+  addExternCSystemInclude(DriverArgs, CC1Args, D.SysRoot + "/include");
+
   addExternCSystemInclude(DriverArgs, CC1Args, D.SysRoot + "/usr/include");
 }