[FFmpeg-cvslog] configure: add linker export script support on Darwin

[Rodger Combs]

ffmpeg | branch: master | Rodger Combs <rodger.combs at gmail.com> | Fri Sep  9 18:12:34 2016 -0500| [63fbeebf6ecb40b21db84d42f9f18867b3f89dca] | committer: Rodger Combs

configure: add linker export script support on Darwin

This isn't a "version script" in the usual sense, since it doesn't set symbol
versions directly. Instead, the version for the whole .dylib is set in the
linker flags, and we generate a list of symbol patterns to export. This allows
us to keep our local symbols (e.g. ff_*) local on the platform.

The Darwin linker's exported_symbols_list format is a bit different than the
one used by the GNU linker. It doesn't handle local symbols at all, since when
a list is provided, all unlisted symbols are local by default; thus, we remove
local sections. It doesn't handle per-version sections, so we remove the
headers and brackets. It expects symbols to be prefixed with an underscore.
It errors if a listed symbol with no wildcards is not present in the output,
so we append an asterisk to any symbol that doesn't already end in one.

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=63fbeebf6ecb40b21db84d42f9f18867b3f89dca
---

 configure | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/configure b/configure
index 2b141fb..ee7e852 100755
--- a/configure
+++ b/configure
@@ -4705,6 +4705,8 @@ case $target_os in
             { check_cflags -mdynamic-no-pic && add_asflags -mdynamic-no-pic; }
         check_header dispatch/dispatch.h &&
             add_cppflags '-I\$(SRC_PATH)/compat/dispatch_semaphore'
+        version_script='-exported_symbols_list'
+        VERSION_SCRIPT_POSTPROCESS_CMD='tr " " "\n" | sed -n /global:/,/local:/p | grep ";" | tr ";" "\n" | sed -E "s/(.+)/_\1/g" | sed -E "s/(.+[^*])$$$$/\1*/"'
         ;;
     msys*)
         die "Native MSYS builds are discouraged, please use the MINGW environment."