[build] Add --divide to ASFLAGS if supported by the assembler

Some builds of the GNU assembler will treat a '/' character as a
comment delimiter.  Adding "--divide" will cause it to be treated as a
division operator, as we expect.  The "--divide" option is not
available in all gas versions, so apply it only conditionally.

Suggested-by: Joshua Oreman <oremanj@rwcr.net>

src/Makefile.housekeeping

@@ -126,6 +126,14 @@ SP_FLAGS := $(shell $(SP_TEST) && $(ECHO) '-fno-stack-protector')
 CFLAGS	+= $(SP_FLAGS)
 endif
 
+# Some versions of gas choke on division operators, treating them as
+# comment markers.  Specifying --divide will work around this problem,
+# but isn't available on older gas versions.
+#
+DIVIDE_TEST = $(AS) --divide /dev/null -o /dev/null 2>/dev/null
+DIVIDE_FLAGS := $(shell $(DIVIDE_TEST) && $(ECHO) '--divide')
+ASFLAGS	+= $(DIVIDE_FLAGS)
+
 ###############################################################################
 #
 # Build verbosity