build: Link game, cgame, ui modules to $(LIBS) (#138)

All three modules call mathematical functions like atan2(). On glibc
systems, when compiled to native code with an ordinary C compiler
(as opposed to bytecode from q3lcc), they get the definition of those
functions from libm.

Until now, they were not explicitly linked to libm, and instead relied
on the fact that libm is linked into the main executable. However,
doing it this way defeats glibc's symbol-versioning mechanisms, and
can fail in some situations, in particular binaries built with
-ffast-math on a pre-2.31 version of glibc (where atan2() resolves to
__atan2_finite()), and used without recompilation on a post-2.31 version
of glibc (where __atan2_finite() has become a deprecated hidden symbol
that is only available as a versioned symbol).

When building shared libraries and loadable modules, it's most robust
to link them explicitly to their dependencies, as is done here.
$(LIBS) also includes -ldl, which is unnecessary but harmless.

Similar to ioquake3 PR <ioquake/ioq3#461>.

Bug-Debian: https://bugs.debian.org/966150
Bug-Debian: https://bugs.debian.org/966173

Makefile

@@ -2320,7 +2320,7 @@ Q3CGVMOBJ = $(Q3CGOBJ_:%.o=%.asm)
 
 $(B)/$(BASEGAME)/cgame$(SHLIBNAME): $(Q3CGOBJ)
 	$(echo_cmd) "LD $@"
-	$(Q)$(CC) $(CFLAGS) $(SHLIBLDFLAGS) -o $@ $(Q3CGOBJ)
+	$(Q)$(CC) $(CFLAGS) $(SHLIBLDFLAGS) -o $@ $(Q3CGOBJ) $(LIBS)
 
 $(B)/$(BASEGAME)/vm/cgame.qvm: $(Q3CGVMOBJ) $(CGDIR)/cg_syscalls.asm $(Q3ASM)
 	$(echo_cmd) "Q3ASM $@"
@@ -2366,7 +2366,7 @@ MPCGVMOBJ = $(MPCGOBJ_:%.o=%.asm)
 
 $(B)/$(MISSIONPACK)/cgame$(SHLIBNAME): $(MPCGOBJ)
 	$(echo_cmd) "LD $@"
-	$(Q)$(CC) $(CFLAGS) $(SHLIBLDFLAGS) -o $@ $(MPCGOBJ)
+	$(Q)$(CC) $(CFLAGS) $(SHLIBLDFLAGS) -o $@ $(MPCGOBJ) $(LIBS)
 
 $(B)/$(MISSIONPACK)/vm/cgame.qvm: $(MPCGVMOBJ) $(CGDIR)/cg_syscalls.asm $(Q3ASM)
 	$(echo_cmd) "Q3ASM $@"
@@ -2429,7 +2429,7 @@ Q3GVMOBJ = $(Q3GOBJ_:%.o=%.asm)
 
 $(B)/$(BASEGAME)/qagame$(SHLIBNAME): $(Q3GOBJ)
 	$(echo_cmd) "LD $@"
-	$(Q)$(CC) $(CFLAGS) $(SHLIBLDFLAGS) -o $@ $(Q3GOBJ)
+	$(Q)$(CC) $(CFLAGS) $(SHLIBLDFLAGS) -o $@ $(Q3GOBJ) $(LIBS)
 
 $(B)/$(BASEGAME)/vm/qagame.qvm: $(Q3GVMOBJ) $(GDIR)/g_syscalls.asm $(Q3ASM)
 	$(echo_cmd) "Q3ASM $@"
@@ -2490,7 +2490,7 @@ MPGVMOBJ = $(MPGOBJ_:%.o=%.asm)
 
 $(B)/$(MISSIONPACK)/qagame$(SHLIBNAME): $(MPGOBJ)
 	$(echo_cmd) "LD $@"
-	$(Q)$(CC) $(CFLAGS) $(SHLIBLDFLAGS) -o $@ $(MPGOBJ)
+	$(Q)$(CC) $(CFLAGS) $(SHLIBLDFLAGS) -o $@ $(MPGOBJ) $(LIBS)
 
 $(B)/$(MISSIONPACK)/vm/qagame.qvm: $(MPGVMOBJ) $(GDIR)/g_syscalls.asm $(Q3ASM)
 	$(echo_cmd) "Q3ASM $@"
@@ -2562,7 +2562,7 @@ Q3UIVMOBJ = $(Q3UIOBJ_:%.o=%.asm)
 
 $(B)/$(BASEGAME)/ui$(SHLIBNAME): $(Q3UIOBJ)
 	$(echo_cmd) "LD $@"
-	$(Q)$(CC) $(CFLAGS) $(SHLIBLDFLAGS) -o $@ $(Q3UIOBJ)
+	$(Q)$(CC) $(CFLAGS) $(SHLIBLDFLAGS) -o $@ $(Q3UIOBJ) $(LIBS)
 
 $(B)/$(BASEGAME)/vm/ui.qvm: $(Q3UIVMOBJ) $(UIDIR)/ui_syscalls.asm $(Q3ASM)
 	$(echo_cmd) "Q3ASM $@"
@@ -2590,7 +2590,7 @@ MPUIVMOBJ = $(MPUIOBJ_:%.o=%.asm)
 
 $(B)/$(MISSIONPACK)/ui$(SHLIBNAME): $(MPUIOBJ)
 	$(echo_cmd) "LD $@"
-	$(Q)$(CC) $(CFLAGS) $(SHLIBLDFLAGS) -o $@ $(MPUIOBJ)
+	$(Q)$(CC) $(CFLAGS) $(SHLIBLDFLAGS) -o $@ $(MPUIOBJ) $(LIBS)
 
 $(B)/$(MISSIONPACK)/vm/ui.qvm: $(MPUIVMOBJ) $(UIDIR)/ui_syscalls.asm $(Q3ASM)
 	$(echo_cmd) "Q3ASM $@"