Effectively revert r151058 which caused Clang's unwind.h to defer to

libunwind in all cases when installed.

At the time, Clang's unwind.h didn't provide huge chunks of the
LSB-specified unwind interface, and was generally too aenemic to use for
real software. However, it has since then become a strict superset of
the APIs provided by libunwind on Linux. Notably, you cannot compile
llgo's libgo library against libunwind, but you can against Clang's
unwind.h. So let's just use our header. =] I've checked pretty
thoroughly for any incompatibilities, and I am not aware of any.

An open question is whether or not we should continue to munge
GNU_SOURCE here. I didn't touch that as it potentially has compatibility
implications on systems I cannot easily test -- Darwin. If a Darwin
maintainer can verify that this is in fact unnecessary and remove it,
cool. Until then, leaving it in makes this change a no-op there, and
only really relevant on Linux systems where it is pretty clearly the
right way to go.

llvm-svn: 224934

1 files changed, 2 insertions, 2 deletions

diff --git a/clang/lib/Headers/unwind.h b/clang/lib/Headers/unwind.h
index d388ef3cb41..90aca16aca3 100644
--- a/clang/lib/Headers/unwind.h
+++ b/clang/lib/Headers/unwind.h
@@ -26,8 +26,8 @@
 #ifndef __CLANG_UNWIND_H
 #define __CLANG_UNWIND_H
 
-#if __has_include_next(<unwind.h>)
-/* Darwin (from 11.x on) and libunwind provide an unwind.h. If that's available,
+#if defined(__APPLE__) && __has_include_next(<unwind.h>)
+/* Darwin (from 11.x on) provide an unwind.h. If that's available,
  * use it. libunwind wraps some of its definitions in #ifdef _GNU_SOURCE,
  * so define that around the include.*/
 # ifndef _GNU_SOURCE