[patch, build] Restore bootstrap in building libcc1 on darwin

[Dominique Dhumieres]

> As I've tried to explain, that is IMHO wrong though.
> If what you are after is the -B stuff too, then perhaps:
> ...

Sorry but it does not work:

true  DO=all multi-do # make
make[4]: Leaving directory '/opt/gcc/build_w/libbacktrace'
make[3]: Leaving directory '/opt/gcc/build_w/libbacktrace'
make[3]: Entering directory '/opt/gcc/build_w/libcpp'
make[3]: Nothing to be done for 'all'.
make[3]: Leaving directory '/opt/gcc/build_w/libcpp'
make[3]: Entering directory '/opt/gcc/build_w/libdecnumber'
make[3]: Nothing to be done for 'all'.
make[3]: Leaving directory '/opt/gcc/build_w/libdecnumber'
make[3]: Entering directory '/opt/gcc/build_w/gcc'
make[3]: Leaving directory '/opt/gcc/build_w/gcc'
Checking multilib configuration for libgcc...
make[3]: Entering directory '/opt/gcc/build_w/x86_64-apple-darwin14.0.0/libgcc'
make[3]: *** No rule to make target ' -B$r/$(TARGET_SUBDIR)/libstdc++-v3/libsupc++/.libs'.  Stop.
make[3]: Leaving directory '/opt/gcc/build_w/x86_64-apple-darwin14.0.0/libgcc'
Makefile:14905: recipe for target 'all-stage1-target-libgcc' failed
make[2]: *** [all-stage1-target-libgcc] Error 2
make[2]: Leaving directory '/opt/gcc/build_w'
Makefile:21193: recipe for target 'stage1-bubble' failed
make[1]: *** [stage1-bubble] Error 2
make[1]: Leaving directory '/opt/gcc/build_w'
Makefile:910: recipe for target 'all' failed
make: *** [all] Error 2

Dominique