Fix macOS build.

There's no <malloc.h> on Darwin. Normally I'd say "prefer <stdlib.h>",
but in this case it looks like the code actually uses memalign. There
is no memalign on Darwin. You'll need to switch to posix_memalign if
you actually care about building this.

For now, the easiest is to just exclude macOS.

Test: treehugger
Change-Id: Id8a11cd141f5c4bd30ce95b61ac64759e17732fc

fuzzer/Android.bp

@@ -8,4 +8,9 @@ cc_fuzz {
         "libavcdec",
         "liblog",
     ],
+    target: {
+        darwin: {
+            enabled: false,
+        },
+    },
 }

test/Android.bp

@@ -16,6 +16,11 @@ cc_test {
     srcs: ["decoder/main.c"],
     static_libs: ["libavcdec"],
     shared_libs: ["liblog"],
+    target: {
+        darwin: {
+            enabled: false,
+        },
+    },
 }
 
 cc_test {