Subzero: Add a --elf arg to szbuild.py and crosstest.py.

pydir/szbuild.py

Index: pydir/szbuild.py
diff --git a/pydir/szbuild.py b/pydir/szbuild.py
index b9e648567472713b326dd1044f009d36043e4f6f..7fcb924514616e59c0b7e64e57d3b9fba0013691 100755
--- a/pydir/szbuild.py
+++ b/pydir/szbuild.py
@@ -80,6 +80,9 @@ def AddOptionalArgs(argparser):
                            help='Optimization level ' +
                                 '(m1 and -1 are equivalent).' +
                                 ' Default %(default)s.')
+    argparser.add_argument('--elf', dest='elf',
+                           action='store_true',
+                           help='Directly generate ELF output')
     argparser.add_argument('--verbose', '-v', dest='verbose',
                            action='store_true',
                            help='Display some extra debugging output')
@@ -202,16 +205,18 @@ def ProcessPexe(args, pexe, exe):
         shellcmd([llvm2ice,
                   '-O' + opt_level,
                   '-bitcode-format=pnacl',
-                  '-o', asm_sz] +
+                  '-o', obj_sz if args.elf else asm_sz] +
                  (['-externalize',
                    '-ffunction-sections',
                    '-fdata-sections'] if hybrid else []) +
+                 (['-elf-writer'] if args.elf else []) +
                  args.sz_args +
                  [pexe],
                  echo=args.verbose)
-        shellcmd((
-            'llvm-mc -arch=x86 -filetype=obj -o {obj} {asm}'
-            ).format(asm=asm_sz, obj=obj_sz), echo=args.verbose)
+        if not args.elf:
+            shellcmd((
+                'llvm-mc -arch=x86 -filetype=obj -o {obj} {asm}'
+                ).format(asm=asm_sz, obj=obj_sz), echo=args.verbose)
         shellcmd((
             'objcopy --redefine-sym _start=_user_start {obj}'
             ).format(obj=obj_sz), echo=args.verbose)