bash 3.2.48: disable parallel build

bash 3.2.48: disable parallel build

It's Makefile has the two rules:
$(BUILTINS_LIBRARY): $(BUILTIN_DEFS) $(BUILTIN_C_SRC) config.h ${BASHINCDIR}/memalloc.h version.h
    @(cd $(DEFDIR) && $(MAKE) $(MFLAGS) DEBUG=${DEBUG} libbuiltins.a ) || exit 1

${DEFDIR}/builtext.h: $(BUILTIN_DEFS)
    @(cd $(DEFDIR) && $(MAKE) $(MFLAGS) builtext.h ) || exit 1

which causes parallel issues:
mkbuiltins.o: file not recognized: File truncated
collect2: ld returned 1 exit status

I don't have any good ideas to fix the problem, so disable parallel
build for it.

Signed-off-by: Robert Yang <liezhi.yang@windriver.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>