Add a postbuild action for executables built with ASan on Mac OS.

build/mac/copy_asan_runtime_dylib.sh

+#!/bin/bash
+
+# For executables built with ASan, copies the runtime lib
+# (libclang_rt.asan_osx_dynamic.dylib) on which they depend from the compiler
+# installation path to the build dir and fixes the dylib's install name in the
+# binary to be relative to @executable_path. This is needed if the executables
+# are copied to a different machine (the ASan runtime library must be copied in
+# this case as well).
+
+set -e
+
+BINARY="${BUILT_PRODUCTS_DIR}/${EXECUTABLE_PATH}"
+BINARY_PATH="$(dirname "${BINARY}")"
+RUNTIME_PATTERN="asan_osx_dynamic.dylib"
+RUNTIME_LIB="$(otool -L "${BINARY}" |
+            grep "${RUNTIME_PATTERN}" |
+            tr -d '\011' |  # remove leading tab
+            sed "s/${RUNTIME_PATTERN}.*/${RUNTIME_PATTERN}/")"
+if [ -z "${RUNTIME_LIB}" ]
+then
+  # TODO(glider): report an error here once we switch to ASan with dynamic
+  # runtime.
+  exit 0
+fi
+
+RUNTIME_FNAME="$(basename "${RUNTIME_LIB}")"
+cp "${RUNTIME_LIB}" "${BINARY_PATH}"
+install_name_tool \
+    -change "${RUNTIME_LIB}" "@executable_path/${RUNTIME_FNAME}" "${BINARY}"