build: Allow building old API/ABI libpostproc version

  Allows our users to still build against a libpostproc with the old
API/ABI. Distributions can use this option to defer the soname bump.
Signed-off-by: Alexander Strasser <eclipse7@gmx.net>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

configure

@@ -262,6 +262,8 @@ Advanced options (experts only):
   --enable-sram            allow use of on-chip SRAM
   --disable-symver         disable symbol versioning
   --optflags               override optimization-related compiler flags
+  --postproc-version=V     build libpostproc version V.
+                           Where V can be '$ALT_PP_VER_MAJOR.$ALT_PP_VER_MINOR.$ALT_PP_VER_MICRO' or 'current'. [$postproc_version_default]
 
 Developer options (useful when working on FFmpeg itself):
   --enable-coverage        build with test coverage instrumentation
@@ -1319,6 +1321,7 @@ CMDLINE_SET="
     target_exec
     target_os
     target_path
+    postproc_version
     valgrind
     yasmexe
 "
@@ -1789,6 +1792,7 @@ incdir_default='${prefix}/include'
 libdir_default='${prefix}/lib'
 mandir_default='${prefix}/share/man'
 shlibdir_default="$libdir_default"
+postproc_version_default="current"
 
 # toolchain
 ar_default="ar"
@@ -1816,6 +1820,12 @@ cpu="generic"
 target_os_default=$(tolower $(uname -s))
 host_os=$target_os_default
 
+# alternative libpostproc version
+ALT_PP_VER_MAJOR=51
+ALT_PP_VER_MINOR=2
+ALT_PP_VER_MICRO=101
+ALT_PP_VER=$ALT_PP_VER_MAJOR.$ALT_PP_VER_MINOR.$ALT_PP_VER_MICRO
+
 # configurable options
 enable $PROGRAM_LIST
 
@@ -2022,7 +2032,17 @@ if enabled cross_compile; then
         die "Must specify target arch and OS when cross-compiling"
 fi
 
-set_default arch target_os
+set_default arch target_os postproc_version
+
+# Check if we should build alternative libpostproc version instead of current
+if   test "$postproc_version" = $ALT_PP_VER; then
+  LIBPOSTPROC_VERSION=$ALT_PP_VER
+  LIBPOSTPROC_VERSION_MAJOR=$ALT_PP_VER_MAJOR
+  LIBPOSTPROC_VERSION_MINOR=$ALT_PP_VER_MINOR
+  LIBPOSTPROC_VERSION_MICRO=$ALT_PP_VER_MICRO
+elif test "$postproc_version" != current; then
+  die "Invalid argument to --postproc-version. See --help output."
+fi
 
 ar_default="${cross_prefix}${ar_default}"
 cc_default="${cross_prefix}${cc_default}"
@@ -3591,8 +3611,11 @@ EOF
 get_version(){
     name=$1
     file=$source_path/$2
+# This condition will be removed when we stop supporting old libpostproc versions
+if ! test "$name" = LIBPOSTPROC || test "$postproc_version" = current; then
     eval $(grep "#define ${name}_VERSION_M" "$file" | awk '{ print $2"="$3 }')
     eval ${name}_VERSION=\$${name}_VERSION_MAJOR.\$${name}_VERSION_MINOR.\$${name}_VERSION_MICRO
+fi
     lcname=$(tolower $name)
     eval echo "${lcname}_VERSION=\$${name}_VERSION" >> config.mak
     eval echo "${lcname}_VERSION_MAJOR=\$${name}_VERSION_MAJOR" >> config.mak
@@ -3669,6 +3692,12 @@ cat > $TMPH <<EOF
 #define AVUTIL_AVCONFIG_H
 EOF
 
+test "$postproc_version" != current && cat >> $TMPH <<EOF
+#define LIBPOSTPROC_VERSION_MAJOR $LIBPOSTPROC_VERSION_MAJOR
+#define LIBPOSTPROC_VERSION_MINOR $LIBPOSTPROC_VERSION_MINOR
+#define LIBPOSTPROC_VERSION_MICRO $LIBPOSTPROC_VERSION_MICRO
+EOF
+
 print_config AV_HAVE_ $TMPH $HAVE_LIST_PUB
 
 echo "#endif /* AVUTIL_AVCONFIG_H */" >> $TMPH

libpostproc/postprocess.h

@@ -29,9 +29,11 @@
 
 #include "libavutil/avutil.h"
 
+#ifndef LIBPOSTPROC_VERSION_MAJOR
 #define LIBPOSTPROC_VERSION_MAJOR 52
 #define LIBPOSTPROC_VERSION_MINOR  0
 #define LIBPOSTPROC_VERSION_MICRO 100
+#endif
 
 #define LIBPOSTPROC_VERSION_INT AV_VERSION_INT(LIBPOSTPROC_VERSION_MAJOR, \
                                                LIBPOSTPROC_VERSION_MINOR, \