Updating re2 build to use -mmic for intel+knc builds

Following the lead of other third-party Makefiles, if we're building for
KNC using the intel compiler, throw the -mmic flag when building re2.
While here, I did some other cleanup:

* broke a long line of commands across several lines
* passed CXX into both recursive make steps just for symmetry (I don't
  believe it's used for the install step)
* removed the set of CC as it doesn't seem to be used by re2's Makefile

Wow, that is weird.  You can see I reformatted without thinking very hard 
about what was there.  Because I fear changing Makefiles on code freeze 
day, I think I'm going to leave this as-is for now and take a TODO to look 
into it later (or, actually, ask whoever implemented it to begin with to 
look into it).

Thanks,
-Brad

On Tue, 16 Sep 2014, Thomas Van Doren wrote:

>> @@ -37,7 +46,13 @@ clobber: FORCE
>>
>>  $(RE2_FILE):
>>  	if [ ! -d re2 ]; then ./unpack-re2.sh; fi
>> -	cd re2 && $(MAKE) clean && $(MAKE) CC=$(CC) CXX=$(CXX) NODEBUG= CXXFLAGS="$(RE_DEBUG_CXX)" && $(MAKE) NODEBUG= CXXFLAGS="$(RE_DEBUG_CXX)" prefix=$(RE2_INSTALL_DIR) install && mkdir -p ../build/$(RE2_UNIQUE_SUBDIR) && rm -rf ../build/$(RE2_UNIQUE_SUBDIR) && mv obj ../build/$(RE2_UNIQUE_SUBDIR)
>> +	cd re2 && \
>> +	$(MAKE) clean && \
>> +	$(MAKE) CXX=$(CXX) NODEBUG= CXXFLAGS="$(RE_DEBUG_CXX) $(CHPL_RE2_CXXFLAGS)" && \
>> +	$(MAKE) CXX=$(CXX) NODEBUG= CXXFLAGS="$(RE_DEBUG_CXX) $(CHPL_RE2_CXXFLAGS)" prefix=$(RE2_INSTALL_DIR) install && \
>> +	mkdir -p ../build/$(RE2_UNIQUE_SUBDIR) && \
>> +	rm -rf ../build/$(RE2_UNIQUE_SUBDIR) && \
>
> I realize this hasn't changed, but it looks like a directory is created and then immediately deleted. Is that necessary? Passing `-f` to `rm` will ensure it succeeds regardless of whether the directory exists or not.
>
> ---
> Reply to this email directly or view it on GitHub:
> https://github.com/chapel-lang/chapel/pull/447/files#r17636716
>