msvc: eliminate spaces in the library search path.

msvc: eliminate spaces in the library search path.

* libltdl/m4/libtool.m4 (_LT_SYS_DYNAMIC_LINKER) [mingw, cygwin]
<cl*, sys_lib_search_path_spec>: The LIB path variable telling
where MSVC looks for libraries is likely to contain directory
names with spaces.  Convert those directory names to the short
8.3 DOS form (i.e. without spaces) when storing them in
sys_lib_search_path_spec, as that is a space separated variable.

Signed-off-by: Peter Rosin <peda@lysator.liu.se>