fix: update libaom POSIX_C_SOURCE patch context for current CMakeLists.txt (#1223)

Author: crazywhalecc

src/globals/patch/libaom_posix_implict.patch

@@ -3,10 +3,10 @@ https://bugs.gentoo.org/869419
 POSIX_C_SOURCE is needed for ftello.
 --- a/CMakeLists.txt
 +++ b/CMakeLists.txt
-@@ -269,6 +269,7 @@ add_library(aom_rtcd OBJECT ${AOM_RTCD_SOURCES})
- add_dependencies(aom_rtcd aom_version)
+@@ -311,6 +311,7 @@ endif()
 
- if(ENABLE_EXAMPLES)
+ if(ENABLE_APPS)
+   # Only used by aomenc.
 +  add_definitions(-D_POSIX_C_SOURCE=200112L)
    add_library(aom_encoder_stats OBJECT ${AOM_ENCODER_STATS_SOURCES})
    set(AOM_LIB_TARGETS ${AOM_LIB_TARGETS} aom_encoder_stats)