Makefile:
- Allow to disable stripping of executables as this prevents from
properly creating debug information sub packages,
- Don't invoke any git commands when building from released
tarball. Moreover, when creating an rpm package with additional
patches then the created git repository is the one in which rpm
applies patches and not the original one.
- Allow to pass CXXFLAGS and LDFLAGS as distributions requires all
packages to be compiled with the same set of flags.
- Support to override DESTDIR when installing files.
- Allow to pass additional arguments (EXTRA_INSTALL_OPTION)
for install.sh script from Makefile.
Signed-off-by: Damian Wrobel <dwrobel@ertelnet.rybnik.pl>