tree bd2fc50b3194f838a51656f8191b7ebd99fb401e
parent 3ee1fe728c53ee07305dcb33177f7de493d108c2
author Reid Kleckner <rnk@google.com> 1570741465 +0000
committer Reid Kleckner <rnk@google.com> 1570741465 +0000

Add -fgnuc-version= to control __GNUC__ and other GCC macros

I noticed that compiling on Windows with -fno-ms-compatibility had the
side effect of defining __GNUC__, along with __GNUG__, __GXX_RTTI__, and
a number of other macros for GCC compatibility. This is undesirable and
causes Chromium to do things like mix __attribute__ and __declspec,
which doesn't work. We should have a positive language option to enable
GCC compatibility features so that we can experiment with
-fno-ms-compatibility on Windows. This change adds -fgnuc-version= to be
that option.

My issue aside, users have, for a long time, reported that __GNUC__
doesn't match their expectations in one way or another. We have
encouraged users to migrate code away from this macro, but new code
continues to be written assuming a GCC-only environment. There's really
nothing we can do to stop that. By adding this flag, we can allow them
to choose their own adventure with __GNUC__.

This overlaps a bit with the "GNUMode" language option from -std=gnu*.
The gnu language mode tends to enable non-conforming behaviors that we'd
rather not enable by default, but the we want to set things like
__GXX_RTTI__ by default, so I've kept these separate.

Helps address PR42817

Reviewed By: hans, nickdesaulniers, MaskRay

Differential Revision: https://reviews.llvm.org/D68055

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@374449 91177308-0d34-0410-b5e6-96231b3b80d8