Ignore deliberate free() of non-heap memory

Bug: http://b/181927912

Clang already has -Wfree-nonheap-object but it became a default warning
with clang-r416183

Test: compile crasher.cpp
Change-Id: Ice532e9f373a628e07acd08a4fc7bfa7cf5d4e08

debuggerd/crasher/Android.bp

@@ -13,7 +13,6 @@ cc_defaults {
         "-Werror",
         "-O0",
         "-fstack-protector-all",
-        "-Wno-free-nonheap-object",
         "-Wno-date-time",
     ],
     srcs: ["crasher.cpp"],

debuggerd/crasher/crasher.cpp

@@ -134,10 +134,14 @@ noinline int crash(int a) {
     return a*2;
 }
 
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wfree-nonheap-object"
+
 noinline void abuse_heap() {
     char buf[16];
     free(buf); // GCC is smart enough to warn about this, but we're doing it deliberately.
 }
+#pragma clang diagnostic pop
 
 noinline void leak() {
     while (true) {