build-sys: introduce a special build flag to explicitly disables running from build...

build-sys: introduce a special build flag to explicitly disables running from build tree

It is helpful to improve reproducibility build [1] since
PA_SRCDIR/PA_BUILDDIR contains build path,
--disable-running-from-build-tree could drop these macros at
precompilation.

[1] https://reproducible-builds.org/

Signed-off-by: Hongxu Jia <hongxu.jia@windriver.com>