build: New configure option '--disable-bootstrap'.

If configure is run with '--disable-bootstrap', then stage1flex won't
be built and stage1scan.c will be generated by sed'ing scan.c.

This option is intended to workaround bootstrap bugs rather than to
fix the bootstrapping issues which are proving subtler and harder to
fix than anyone would like.

configure.ac

@@ -66,6 +66,15 @@ AC_ARG_ENABLE([libfl],
   [], [enable_libfl=yes])
 AM_CONDITIONAL([ENABLE_LIBFL], [test "x$enable_libfl" = xyes])
 
+# --disable-bootstrap is intended only to workaround problems with bootstrap
+# (e.g. when cross-compiling flex or when bootstrapping has bugs).
+# Ideally we should be able to bootstrap even when cross-compiling.
+AC_ARG_ENABLE([bootstrap],
+  [AS_HELP_STRING([--disable-bootstrap],
+                  [don't perform a bootstrap when building flex])],
+  [], [enable_bootstrap=yes])
+AM_CONDITIONAL([ENABLE_BOOTSTRAP], [test "x$enable_bootstrap" = xyes])
+
 AC_PATH_PROG([BISON], bison, no)
 AS_IF([test "$BISON" != no],[],
 	[ AC_SUBST([BISON], [\${top_srcdir}/build-aux/missing bison])

src/Makefile.am

@@ -6,7 +6,9 @@ LIBS = @LIBS@
 m4 = @M4@
 
 bin_PROGRAMS = flex
+if ENABLE_BOOTSTRAP
 noinst_PROGRAMS = stage1flex
+endif
 
 if ENABLE_LIBFL
 lib_LTLIBRARIES = libfl.la
@@ -82,16 +84,21 @@ skel.c: flex.skl mkskel.sh flexint.h tables_shared.h tables_shared.c
 	  $(SHELL) $(srcdir)/mkskel.sh > $@.tmp
 	mv $@.tmp $@
 
+if ENABLE_BOOTSTRAP
 stage1scan.c: scan.l stage1flex$(EXEEXT)
 	./stage1flex$(EXEEXT) $(AM_LFLAGS) $(LFLAGS) -o $@ $<
+else
+stage1scan.c: scan.c
+	sed 's|^\(#line .*\)"'`printf %s $< | sed 's|[][\\\\.*]|\\\\&|g'`'"|\1"$@"|g' $< > $@
+endif
 
 # make needs to be told to make parse.h so that parallelized runs will
 # not fail.
 
-main.c : parse.h
-scan.c : parse.h
-stage1scan.c : parse.h
-yylex.c : parse.h
+main.c: parse.h
+yylex.c: parse.h
+stage1flex-scan.$(OBJEXT): parse.h
+flex-stage1scan.$(OBJEXT): parse.h
 
 # Run GNU indent on sources. Don't run this unless all the sources compile cleanly.
 #