That "revision" was inherited from SVN days but had been since then
used to give information about the build: "custom_build", "official",
"<some distro's build>".
It can now be overridden with the BUILD_NAME environment variable.
Removes the need for _MKSTR all over the place which has the drawback of
converting _MKSTR(UNKNOWN_DEFINE) to "UKNOWN_DEFINE" instead of throwing
a compilation error.
Fixes a bug where the VERSION_PATCH define is not yet in scope if
typedefs.h is included before version.h at compilation time.
(cherry picked from commit 3b687c5474)
