Simplify makefile boilerplate code.

Don't define ASM_SOURCES variable globally -- reserve that variable to be defined
locally by makefiles, together with C_SOURCES and CPP_SOURCES.
diff --git a/configs/sunos5-gcc b/configs/sunos5-gcc
index 77b293c..3fa13d0 100644
--- a/configs/sunos5-gcc
+++ b/configs/sunos5-gcc
@@ -16,8 +16,8 @@
 
 DEFINES = -D_REENTRANT -DUSE_XSHM
 
-ASM_SOURCES = $(SPARC_SOURCES)
-ASM_API = $(SPARC_API)
+MESA_ASM_SOURCES = $(SPARC_SOURCES)
+GLAPI_ASM_SOURCES = $(SPARC_API)
 ASM_FLAGS = -DUSE_SPARC_ASM
 
 CFLAGS   = $(WARN_FLAGS) $(OPT_FLAGS) $(PIC_FLAGS) $(ARCH_FLAGS) $(DEFINES) \