[build][mips] Include libatomic when building for mips

NOTRY=true

Bug: v8:8291
Change-Id: Iae948ef9de027f86702accf34487524fd1c6b538
Reviewed-on: https://chromium-review.googlesource.com/c/1296455
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Reviewed-by: Sergiy Byelozyorov <sergiyb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56898}

infra/mb/mb_config.pyl

@@ -662,7 +662,10 @@
     },
 
     'mips_bundled_toolchain': {
-      'gn_args': 'custom_toolchain="//tools/toolchain:mips-bundled"',
+      'gn_args': 'custom_toolchain="//tools/toolchain:mips-bundled" '
+                 'ldso_path="//tools/mips_toolchain/sysroot/usr/lib/ld.so.1" '
+                 'gcc_target_rpath="//tools/mips_toolchain/sysroot/usr/lib:'
+                 '//tools/mips_toolchain/mips-mti-linux-gnu/lib:\$ORIGIN/."',
     },
 
     'msan': {