Partially revert "automake: allow only shared builds"

Evidently at least static OSMesa is still used as shared one
causes substantial increase in the load time for some programs
that use it (from seconds up-to ~30min).

Rather than forcing everyone to use shared mesa, revert commit
a6efbac9fb and default to shared
build when both shared and static are disabled.

v2: Whitespace cleanup, drop silly comment.

Reported-by: Burlen Loring <burlen.loring@gmail.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>

install-gallium-links.mk

@@ -1,6 +1,7 @@
 # Provide compatibility with scripts for the old Mesa build system for
 # a while by putting a link to the driver into /lib of the build tree.
 
+if BUILD_SHARED
 if HAVE_COMPAT_SYMLINKS
 all-local : .libs/install-gallium-links
 
@@ -23,3 +24,4 @@ all-local : .libs/install-gallium-links
 		fi;						\
 	done && touch $@
 endif
+endif