[cairo] [PATCH v2 2/3] configure.ac: Add a --disable-lto configure option

[Bryce W. Harrington]

Link-Time Optimization seems to be stable enough with gcc 4.8 and 4.9,
but has proven to be an issue in the past for many cairo users (webkit,
efl, ubuntu, opensuse, gentoo, arch...) who carry patches to disable it.

Gentoo's patch[1] adds a --disable-lto option to leave it enabled by
default but give users the ability to work around lto related build
problems (c.f. fdo #77060).  Patch appears to have been authored by
Alexandre Rostovtsev[2].

1: sources.gentoo.org/cgi-bin/viewvc.cgi/gentoo-x86/x11-libs/cairo/files/cairo-1.12.16-lto-optional.patch
2: https://bugs.gentoo.org/show_bug.cgi?id=509552

Fixes: https://bugs.freedesktop.org/show_bug.cgi?id=60852
Signed-off-by: Bryce Harrington <b.harrington at samsung.com>
Reviewed-by: Uli Schlachter <psychon at znc.in>
---
 build/configure.ac.warnings | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/build/configure.ac.warnings b/build/configure.ac.warnings
index f984eb2..a72d948 100644
--- a/build/configure.ac.warnings
+++ b/build/configure.ac.warnings
@@ -38,13 +38,18 @@ dnl options.  Namely, the following:
 
 dnl -flto working really needs a test link, not just a compile
 
-safe_MAYBE_WARN="$MAYBE_WARN"
-MAYBE_WARN="$MAYBE_WARN -flto"
-AC_TRY_LINK([],[
+AC_ARG_ENABLE(lto,
+  AS_HELP_STRING([--disable-lto],
+                 [Do not try to use Link-Time Optimization]))
+if test "x$enable_lto" != "xno"; then
+   safe_MAYBE_WARN="$MAYBE_WARN"
+   MAYBE_WARN="$MAYBE_WARN -flto"
+   AC_TRY_LINK([],[
 	int main(int argc, char **argv) { return 0; }
-],[],[
+   ],[],[
 	MAYBE_WARN="$safe_MAYBE_WARN"
-])
+   ])
+fi
 
 MAYBE_WARN="$MAYBE_WARN -fno-strict-aliasing -fno-common"
 
-- 
1.9.1