contrib: libplacebo: fix build with Android NDK25

execinfo.h is present but not necessary the functions (backtrace())
since it depends on the configured ANDROID_API.

It's not a clean and "upstreamable" patch, but the execinfo code is gone
upstream, so this patch is only temporary.

contrib/src/libplacebo/fix-android-build.patch

+diff -Naur libplacebo/src/meson.build libplacebo.new/src/meson.build
+--- libplacebo/src/meson.build	2022-02-03 16:30:55.000000000 +0100
++++ libplacebo.new/src/meson.build	2022-07-22 08:22:49.573761162 +0200
+@@ -69,7 +69,7 @@
+ endif
+ 
+ unwind = dependency('libunwind', required: get_option('unwind'))
+-has_execinfo = cc.has_header('execinfo.h')
++has_execinfo = false
+ conf_internal.set('PL_HAVE_UNWIND', unwind.found())
+ conf_internal.set('PL_HAVE_EXECINFO', has_execinfo)
+ if unwind.found()

contrib/src/libplacebo/rules.mak

@@ -37,6 +37,9 @@ libplacebo: $(PLACEBO_ARCHIVE) .sum-libplacebo
 	$(UNPACK)
 	$(APPLY) $(SRC)/libplacebo/0001-vulkan-blacklist-metal-structs-from-utils_gen.py.patch
 	$(APPLY) $(SRC)/libplacebo/0002-pl_thread-use-gettimeofday-for-back-compat.patch
+ifdef HAVE_ANDROID
+	$(APPLY) $(SRC)/libplacebo/fix-android-build.patch
+endif
 	$(MOVE)
 
 .libplacebo: libplacebo crossfile.meson