Allow AsmLabel with -fno-gnu-inline-asm

Summary:
AsmLabel is heavily used in system level and firmware to redirect
function and access platform specific labels. They are also extensively
used in system headers which makes this option unusable for many
users. Since AsmLabel doesn't introduce any assembly code into the
output binary, it shouldn't be considered as inline-asm.

Reviewers: bob.wilson, rnk

Reviewed By: rnk

Subscribers: cfe-commits

Differential Revision: http://reviews.llvm.org/D9679

llvm-svn: 237048