Set ASAN_SYMBOLIZER_PATH

So that we get symbolized backtraces when possible.

Test: trigger segfault in ninja_test; see symbolized backtrace
Change-Id: I1e28044a3b7a4bb95a4ed35d41ccd36f3bec4e4a
diff --git a/build-prebuilts.sh b/build-prebuilts.sh
index 5f3697d..b12d3c6 100755
--- a/build-prebuilts.sh
+++ b/build-prebuilts.sh
@@ -130,6 +130,8 @@
 }
 EOF
 
+        export ASAN_SYMBOLIZER_PATH=${PWD}/prebuilts/clang/host/linux-x86/llvm-binutils-stable/llvm-symbolizer
+
         # Clean up non-ASAN installed versions
         rm -rf ${SOONG_HOST_OUT}