build: Only build libmesa.la when needed

Namely, for Xlib-GLX, OSMesa, or test programs.

configure.ac

@@ -699,6 +699,8 @@ if test "x$enable_glx" = xyes -a \
 fi
 
 AM_CONDITIONAL(HAVE_DRI, test "x$enable_dri" = xyes)
+AM_CONDITIONAL(NEED_LIBMESA, test "x$enable_xlib_glx" = xyes -o \
+                                  "x$enable_osmesa" = xyes)
 
 AC_ARG_ENABLE([shared-glapi],
     [AS_HELP_STRING([--enable-shared-glapi],

src/mesa/Makefile.am

@@ -94,7 +94,12 @@ program/lex.yy.c: program/program_lexer.l
 	$(MKDIR_P) program
 	$(AM_V_GEN) $(LEX) --never-interactive --outfile=$@ $<
 
-noinst_LTLIBRARIES = libmesa.la
+noinst_LTLIBRARIES =
+if NEED_LIBMESA
+noinst_LTLIBRARIES += libmesa.la
+else
+check_LTLIBRARIES = libmesa.la
+endif
 if HAVE_GALLIUM
 noinst_LTLIBRARIES += libmesagallium.la
 endif
@@ -145,15 +150,14 @@ libmesagallium_la_SOURCES = \
 libmesagallium_la_LIBADD = $(top_builddir)/src/glsl/libglsl.la
 libmesagallium_la_LDFLAGS =
 
+if HAVE_GALLIUM
 # Provide compatibility with scripts for the old Mesa build system for
 # a while by putting a link to the library in the current directory.
 all-local: $(noinst_LTLIBRARIES)
-	ln -f .libs/libmesa.a .
-if HAVE_GALLIUM
 	ln -f .libs/libmesagallium.a .
 endif
 
-CLEANFILES += libmesa.a libmesagallium.a
+CLEANFILES += libmesagallium.a
 
 pkgconfigdir = $(libdir)/pkgconfig
 pkgconfig_DATA = gl.pc