Add source map for binaries from RBE

Binaries built from RBE are using a source path under /b/f/w. Also map that to local source path.

Test: lldbclient.py -r /system/bin/ls
Change-Id: I02a90a9c827189a14b2d83485ed2abda68f9e084
diff --git a/scripts/gdbclient.py b/scripts/gdbclient.py
index d7c8ecb..639f6e9 100755
--- a/scripts/gdbclient.py
+++ b/scripts/gdbclient.py
@@ -351,7 +351,9 @@
         'settings append target.exec-search-paths {}'.format(' '.join(solib_search_path)))
 
     commands.append('target create {}'.format(binary_name))
-    commands.append("settings set target.source-map '' '{}'".format(root))
+    # For RBE support.
+    commands.append("settings append target.source-map '/b/f/w' '{}'".format(root))
+    commands.append("settings append target.source-map '' '{}'".format(root))
     commands.append('target modules search-paths add / {}/'.format(sysroot))
     commands.append('gdb-remote {}'.format(port))
     return '\n'.join(commands)