After applying hash 43662968, gdb.1 and other man pages are not added
target triplet even if we configure with --target=.
It causes conflicts on some distributions.
And uninstall rules requires $(transform) variable.
gdb/doc/ChangeLog:
* Makefile.in (transform): New variable.
(install-man1, install-man5): Apply $(transform) to man file names.
Tested by installing both native and cross debugger.
90debf20f4
