work around constant folding bug 61144 in gcc 4.9.0 and 4.9.1

previously we detected this bug in configure and issued advice for a
workaround, but this turned out not to work. since then gcc 4.9.0 has
appeared in several distributions, and now 4.9.1 has been released
without a fix despite this being a wrong code generation bug which is
supposed to be a release-blocker, per gcc policy.

since the scope of the bug seems to affect only data objects (rather
than functions) whose definitions are overridable, and there are only
a very small number of these in musl, I am just changing them from
const to volatile for the time being. simply removing the const would
be sufficient to make gcc 4.9.1 work (the non-const case was
inadvertently fixed as part of another change in gcc), and this would
also be sufficient with 4.9.0 if we forced -O0 on the affected files
or on the whole build. however it's cleaner to just remove all the
broken compiler detection and use volatile, which will ensure that
they are never constant-folded. the quality of a non-broken compiler's
output should not be affected except for the fact that these objects
are no longer const and thus possibly add a few bytes to data/bss.

this change can be reconsidered and possibly reverted at some point in
the future when the broken gcc versions are no longer relevant.

1 files changed, 1 insertions, 1 deletions

diff --git a/src/stdio/stdin.c b/src/stdio/stdin.c
index 476dc708..171ff22a 100644
--- a/src/stdio/stdin.c
+++ b/src/stdio/stdin.c
@@ -12,4 +12,4 @@ static FILE f = {
 	.lock = -1,
 };
 FILE *const stdin = &f;
-FILE *const __stdin_used = &f;
+FILE *volatile __stdin_used = &f;