Revert of PPC/s390: [sysroot installer] Disable for host arch PPC/s390 (patchset #3 id:40001 of https://codereview.chromium.org/2368943005/ )

Reason for revert:
This causes failures in gclient runhooks on 32 bit machines:

https://build.chromium.org/p/chromium.win/builders/Win7%20%2832%29%20Tests/builds/10626

Log snippet:

running 'E:\b\depot_tools\python276_bin\python.exe src/build/linux/sysroot_scripts/install-sysroot.py
Unrecognized host arch: x86

Original issue's description:
> 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.
>
> R=agrieve@chromium.org
>
> BUG=
> LOG=N
>
> Committed: https://crrev.com/5e5689bba0a51bad28c08bf3a3820da57a185c3b
> Cr-Commit-Position: refs/heads/master@{#421722}

TBR=agrieve@chromium.org,bjaideep@ca.ibm.com
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=

Review-Url: https://codereview.chromium.org/2376253002
Cr-Original-Commit-Position: refs/heads/master@{#421735}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 9cc67cbe3ea5b54c3fc8f6793e947150182f3c2b

detect_host_arch.py

@@ -17,17 +17,12 @@ def HostArch():
   # Convert machine type to format recognized by gyp.
   if re.match(r'i.86', host_arch) or host_arch == 'i86pc':
     host_arch = 'ia32'
-  elif host_arch in ['x86_64', 'amd64', 'AMD64']:
+  elif host_arch in ['x86_64', 'amd64']:
     host_arch = 'x64'
   elif host_arch.startswith('arm'):
     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.

linux/sysroot_scripts/install-sysroot.py

@@ -108,10 +108,6 @@ def DetectHostArch():
     return 'arm64'
   elif detected_host_arch == 'mips':
     return 'mips'
-  elif detected_host_arch == 'ppc':
-    return 'ppc'
-  elif detected_host_arch == 's390':
-    return 's390'
 
   raise Error('Unrecognized host arch: %s' % detected_host_arch)
 
@@ -182,14 +178,9 @@ def main(args):
   parser.add_option('--arch', type='choice', choices=valid_archs,
                     help='Sysroot architecture: %s' % ', '.join(valid_archs))
   options, _ = parser.parse_args(args)
-  host_arch = DetectHostArch()
   if options.running_as_hook and not sys.platform.startswith('linux'):
     return 0
 
-  # PPC/s390 don't use sysroot, see http://crbug.com/646169
-  if host_arch in ('ppc','s390'):
-    return 0
-
   if options.running_as_hook:
     InstallDefaultSysroots()
   else: