Darwin install strips all global symbols, which gives undefined symbols

when linking against a stripped library.  To avoid this, an installstrip
variable is added that can be overridden on a per-OS basis.
patch by Steven M. Schultz < sms == at -- 2BSD -- dot == COM >

Originally committed as revision 4656 to svn://svn.ffmpeg.org/ffmpeg/trunk

configure

@@ -205,6 +205,7 @@ lshared="no"
 optimize="yes"
 debug="yes"
 dostrip="yes"
+installstrip="-s"
 extralibs="-lm"
 simpleidct="yes"
 bigendian="no"
@@ -333,6 +334,7 @@ SHFLAGS="-dynamiclib -Wl,-single_module,-undefined,dynamic_lookup"
 extralibs=""
 darwin="yes"
 strip="strip -x"
+installstrip=""
 LDFLAGS="-Wl,-dynamic,-search_paths_first"
 SLIBSUF=".dylib"
 FFSLDFLAGS=-Wl,-bind_at_load
@@ -1286,7 +1288,7 @@ echo "AR=$ar" >> config.mak
 echo "RANLIB=$ranlib" >> config.mak
 if test "$dostrip" = "yes" ; then
 echo "STRIP=$strip" >> config.mak
-echo "INSTALLSTRIP=-s" >> config.mak
+echo "INSTALLSTRIP=$installstrip" >> config.mak
 else
 echo "STRIP=echo ignoring strip" >> config.mak
 echo "INSTALLSTRIP=" >> config.mak