Use lowercase machine architecture.

Bug: 896355
Change-Id: I83a3c27478029d90206b5bb26e26797df47a90f6
Reviewed-on: https://chromium-review.googlesource.com/c/1287244
Reviewed-by: Andrii Shyshkalov <tandrii@chromium.org>
Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>

detect_host_arch.py

@@ -12,7 +12,7 @@ import sys
 
 def HostArch():
   """Returns the host architecture with a predictable string."""
-  host_arch = platform.machine()
+  host_arch = platform.machine().lower()
 
   # Convert machine type to format recognized by gyp.
   if re.match(r'i.86', host_arch) or host_arch == 'i86pc':