scripts: PARALLELMFLAGS is evil, rename

The reunification of the glibc/eglibc code paths exposed a nasty
bug in the glibc build: use of PARALLELMFLAGS breaks the build.

See the explanations in that bug report against FC6:
https://bugzilla.redhat.com/show_bug.cgi?format=multiple&id=212111

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

 reporter_name="Yann E. MORIN"

 reporter_url="http://ymorin.is-a-geek.org/projects/crosstool"

 reporter_comment="Experimental toolchain for ARM cortex-m3 in Thumb-only, noMMU, and newlib."