root: fix compiledata.h CXX; add armv7 support

ROOT build scripts fails to set CXX and MAKESHAREDLIB while generating
compiledata.h header if CXX is set on make command.

Add ARMv7 support in Cintex and configure script. This uses less
invasive implementation then previous.

Signed-off-by: David Abdurachmanov <David.Abdurachmanov@cern.ch>