zos: build with -m64 and ignore unknown-pragmas

- Explicitly pass -m64 as CC/CXX can be clang/clang++
  or ibm-clang/ibm-clang++ rather than their 64-suffixed names.
- Ignore unknown-pragma errors as some system headers include
  pragmas not yet supported by the clang compiler (e.g.
  #pragma checkout(suspend|resume).
- Remove 'install/' from the ZOSLIB default path, as it may not be
  inside such directory.

Change-Id: I2857a1b3a095c96d92c288d0212c70852bf46b64
Reviewed-on: https://gn-review.googlesource.com/c/gn/+/18460
Reviewed-by: Takuto Ikuta <tikuta@google.com>
Commit-Queue: David Turner <digit@google.com>
Reviewed-by: David Turner <digit@google.com>

build/gen.py

diff --git a/build/gen.py b/build/gen.py
index cdee2f5..8470373 100755
--- a/build/gen.py
+++ b/build/gen.py
@@ -206,8 +206,8 @@
                       default='../third_party/zoslib',
                       dest='zoslib_dir',
                       help=('Specify the path of ZOSLIB directory, to link ' +
-                            'with <ZOSLIB_DIR>/install/lib/libzoslib.a, and ' +
-                            'add -I<ZOSLIB_DIR>/install/include to the compile ' +
+                            'with <ZOSLIB_DIR>/lib/libzoslib.a, and ' +
+                            'add -I<ZOSLIB_DIR>/include to the compile ' +
                             'commands. See README.md for details.'))
 
   args_list.add_to_parser(parser)
@@ -417,7 +417,7 @@
       '.',
   ]
   if platform.is_zos():
-    include_dirs += [ options.zoslib_dir + '/install/include' ]
+    include_dirs += [ options.zoslib_dir + '/include' ]
 
   libs = []
 
@@ -531,7 +531,10 @@
       cflags.append('-fPIC')
       cflags.extend(['-D_BSD_SOURCE'])
     elif platform.is_zos():
+      cflags.append('-m64')
+      ldflags.append('-m64')
       cflags.append('-fzos-le-char-mode=ascii')
+      cflags.append('-Wno-unknown-pragmas')
       cflags.append('-Wno-unused-function')
       cflags.append('-D_OPEN_SYS_FILE_EXT')
       cflags.append('-DPATH_MAX=1024')
@@ -907,7 +910,7 @@
     ])
 
   if platform.is_zos():
-    libs.extend([ options.zoslib_dir + '/install/lib/libzoslib.a' ])
+    libs.extend([ options.zoslib_dir + '/lib/libzoslib.a' ])
 
   if platform.is_windows():
     static_libraries['base']['sources'].extend([