Allow different --libtool options from multiple gnulib-tool invocations.
* gnulib-local/modules/libxml (Makefile.am): Don't test GL_COND_LIBTOOL, since
gnulib-tool already eliminates lib_LDFLAGS augmentations for non-libtool
libraries.
* libtextstyle/gnulib-local/modules/libcroco (Makefile.am): Likewise.
* libtextstyle/gnulib-local/modules/libglib (Makefile.am): Likewise.