[build] Fix build configs for win-asan

Win asan needs separate "clang" config as clang is not the default on windows.

TBR=sergiyb@chromium.org
NOTRY=true

Bug: chromium:726584
Change-Id: Ic49eedf9a229eb3f81774c8d03c9d19ba1211c3d
Reviewed-on: https://chromium-review.googlesource.com/720801Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48576}

infra/mb/mb_config.pyl

@@ -489,7 +489,7 @@
     'gn_release_x86': [
       'gn', 'release_bot', 'x86', 'swarming'],
     'gn_release_x86_asan_no_lsan': [
-      'gn', 'release_bot', 'x86', 'asan', 'swarming'],
+      'gn', 'release_bot', 'x86', 'asan', 'clang', 'swarming'],
     'gn_release_x86_disassembler': [
       'gn', 'release_bot', 'x86', 'v8_enable_disassembler'],
     'gn_release_x86_gcc': [