PPC/s390: [sysroot installer] Disable for host arch PPC/s390

Since PPC/s390 doesn't have the sysroot files available
on google storage, disabling it so that the script doesn't
cause gclient sync to fail when run on PPC/s390.

[email protected]

BUG=
LOG=N

Review-Url: https://codereview.chromium.org/2382883003
Cr-Commit-Position: refs/heads/master@{#422014}
diff --git a/build/detect_host_arch.py b/build/detect_host_arch.py
index ccfbb6e..8d6a1ba9 100755
--- a/build/detect_host_arch.py
+++ b/build/detect_host_arch.py
@@ -23,6 +23,11 @@
     host_arch = 'arm'
   elif host_arch.startswith('mips'):
     host_arch = 'mips'
+  elif host_arch.startswith('ppc'):
+    host_arch = 'ppc'
+  elif host_arch.startswith('s390'):
+    host_arch = 's390'
+
 
   # platform.machine is based on running kernel. It's possible to use 64-bit
   # kernel with 32-bit userland, e.g. to give linker slightly more memory.