[hwasan] Add default "/" prefix.

Add a default "/" prefix to the symbol search path in the
symbolization script. Without this, the binary itself is not considered
a valid source of symbol info.

Differential Revision: https://reviews.llvm.org/D111840

compiler-rt/lib/hwasan/scripts/hwasan_symbolize

@@ -200,6 +200,7 @@ if not binary_prefixes:
   if 'ANDROID_PRODUCT_OUT' in os.environ:
     product_out = os.path.join(os.environ['ANDROID_PRODUCT_OUT'], 'symbols')
     binary_prefixes.append(product_out)
+  binary_prefixes.append('/')
 
 for p in binary_prefixes:
   if not os.path.isdir(p):