Hard-code build-aux/install-sh in all install scripts

Hard-code build-aux/install-sh in all install scripts
instead of relying on @INSTALL@ to pick an install executable
on systems where @INSTALL@ resolves, ends up picking the system preferred install
which at least on mingw64 won't directories if they don't exist
in addition on mingw64, it doesn't
even fill in @INSTALL@ with install unless AC_PROG_INSALL is included
References #3916 for PostGIS 2.5 (trunk)
References #3912 for PostGIS 2.5 (trunk)

git-svn-id: http://svn.osgeo.org/postgis/trunk@16073 b70326c6-7e19-0410-871a-916f4a2858ee