Add a '-E' option to the test driver for the purpose of specifying some extra CFLAGS

to pass to the toolchain in order to build the inferior programs to be run/debugged
duirng the test suite.  The architecture might dictate some special CFLAGS which are
more easily specified in a central place (like the command line) instead of inside
make rules.

For Example,

./dotest.py -v -r /shared/phone -A armv7 -E "-isysroot your_sdk_root" functionalities/watchpoint/hello_watchpoint

will relocate the particular test directory ('functionalities/watchpoint/hello_watchpoint' in this case) to a
new directory named '/shared/phone'.  The particular incarnation of the architecture-compiler combination of the
test support files are therefore to be found under:

/shared/phone.arch=armv7-compiler=clang/functionalities/watchpoint/hello_watchpoint

The building of the inferior programs under testing is now working.

The actual launching/debugging of the inferior programs are not yet working,
neither is the setting of a watchpoint on the phone.

llvm-svn: 153070