Subzero: Change the szbuild.py --force default.

With the --force option, the behavior of its default setting is dangerous.  Specifically, it doesn't retranslate by default when you change the szbuild command-line arguments.  This leads to debugging frustration.

Therefore, we change the default setting to be "dumb" and always retranslate.

For bisection debugging, the user will quickly realize that they want to add "--force=0".

BUG= none
R=jpp@chromium.org

Review URL: https://codereview.chromium.org/1608323002 .

Makefile.standalone

diff --git a/Makefile.standalone b/Makefile.standalone
index 9f6e655..38e7bd9 100644
--- a/Makefile.standalone
+++ b/Makefile.standalone
@@ -473,7 +473,7 @@
 SPECFLAGS :=
 SPECBUILDONLY := false
 %.spec2k: % $(OBJDIR)/pnacl-sz make_symlink runtime
-	./pydir/szbuild_spec2k.py -v --force \
+	./pydir/szbuild_spec2k.py -v \
           $(SPECFLAGS) --target=$(TARGETFLAG) $(SPEC) $<
 	$(SPECBUILDONLY) || ( cd ../../../tests/spec2k; \
 	 ./run_all.sh RunTimedBenchmarks $(SETUP) train $< )

pydir/szbuild.py

diff --git a/pydir/szbuild.py b/pydir/szbuild.py
index 5f645b8..36112da 100755
--- a/pydir/szbuild.py
+++ b/pydir/szbuild.py
@@ -61,8 +61,10 @@
     return default_match
 
 def AddOptionalArgs(argparser):
-    argparser.add_argument('--force', dest='force', action='store_true',
-                           help='Force all re-translations of the pexe')
+    argparser.add_argument('--force', dest='force', type=int, choices=[0, 1],
+                           default=1,
+                           help='Force all re-translations of the pexe.' +
+                                ' Default %(default)s.')
     argparser.add_argument('--include', '-i', default=[], dest='include',
                            action='append',
                            help='Subzero symbols to include ' +
@@ -240,11 +242,11 @@
     If no --include or --exclude arguments are given, the executable is produced
     entirely using Subzero, without using llc or linker tricks.
 
-    This script uses file modification timestamps to determine whether llc and
-    Subzero re-translation are needed.  It checks timestamps of llc, pnacl-sz,
-    and the pexe against the translated object files to determine the minimal
-    work necessary.  The --force option suppresses those checks and
-    re-translates everything.
+    When using the --force=0 option, this script uses file modification
+    timestamps to determine whether llc and Subzero re-translation are needed.
+    It checks timestamps of llc, pnacl-sz, and the pexe against the translated
+    object files to determine the minimal work necessary.  The --force=1 option
+    (default) suppresses those checks and re-translates everything.
 
     This script expects various PNaCl and LLVM tools to be found within the
     native_client tree.  When changes are made to these tools, copy them this