[Driver] Add support for -finline-functions and /Ob2 flags

-finline-functions and /Ob2 are currently ignored by Clang. The only way to
enable inlining is to use the global O flags, which also enable other options,
or to emit LLVM bitcode using Clang, then running opt by hand with the inline
pass.

This patch allows to simply use the -finline-functions flag (same as GCC) or
/Ob2 in clang-cl mode to enable inlining without other optimizations.

This is the first patch of a serie to improve support for the /Ob flags.

Patch by Rudy Pons <rudy.pons@ilod.org>!

Differential Revision: http://reviews.llvm.org/D20576

llvm-svn: 270609
diff --git a/clang/test/Driver/cl-options.c b/clang/test/Driver/cl-options.c
index 02e6243..6a721fc 100644
--- a/clang/test/Driver/cl-options.c
+++ b/clang/test/Driver/cl-options.c
@@ -97,6 +97,9 @@
 // RUN: %clang_cl /Ob0 -### -- %s 2>&1 | FileCheck -check-prefix=Ob0 %s
 // Ob0: -fno-inline
 
+// RUN: %clang_cl /Ob2 -### -- %s 2>&1 | FileCheck -check-prefix=Ob2 %s
+// Ob2: -finline-functions
+
 // RUN: %clang_cl /Od -### -- %s 2>&1 | FileCheck -check-prefix=Od %s
 // Od: -O0
 
@@ -265,7 +268,6 @@
 // RUN:    /kernel- \
 // RUN:    /nologo \
 // RUN:    /Ob1 \
-// RUN:    /Ob2 \
 // RUN:    /openmp- \
 // RUN:    /RTC1 \
 // RUN:    /sdl \