build: add rules to generate preprocessed source files

This is useful for debugging.  Dependencies for these files are not
generated due to limitations in many compilers.
Signed-off-by: NMans Rullgard <mans@mansr.com>

Makefile

@@ -45,6 +45,9 @@ COMPILE_S = $(call COMPILE,AS)
 %.o: %.S
 	$(COMPILE_S)
 
+%.i: %.c
+	$(CC) $(CCFLAGS) $(CC_E) $<
+
 %.h.c:
 	$(Q)echo '#include "$*.h"' >$@
 

configure

@@ -3756,6 +3756,7 @@ ASFLAGS=$ASFLAGS
 AS_C=$AS_C
 AS_O=$AS_O
 CC_C=$CC_C
+CC_E=$CC_E
 CC_O=$CC_O
 LD_O=$LD_O
 LD_LIB=$LD_LIB

library.mak

@@ -17,12 +17,19 @@ $(SUBDIR)%-test.o: $(SUBDIR)%-test.c
 $(SUBDIR)%-test.o: $(SUBDIR)%.c
 	$(COMPILE_C)
 
+$(SUBDIR)%-test.i: $(SUBDIR)%-test.c
+	$(CC) $(CCFLAGS) $(CC_E) $<
+
+$(SUBDIR)%-test.i: $(SUBDIR)%.c
+	$(CC) $(CCFLAGS) $(CC_E) $<
+
 $(SUBDIR)x86/%.o: $(SUBDIR)x86/%.asm
 	$(DEPYASM) $(YASMFLAGS) -I $(<D)/ -M -o $@ $< > $(@:.o=.d)
 	$(YASM) $(YASMFLAGS) -I $(<D)/ -o $@ $<
 
-$(OBJS) $(SUBDIR)%.h.o $(TESTOBJS): CPPFLAGS += -DHAVE_AV_CONFIG_H
-$(TESTOBJS): CPPFLAGS += -DTEST
+LIBOBJS := $(OBJS) $(SUBDIR)%.h.o $(TESTOBJS)
+$(LIBOBJS) $(LIBOBJS:.o=.i):   CPPFLAGS += -DHAVE_AV_CONFIG_H
+$(TESTOBJS) $(TESTOBJS:.o=.i): CPPFLAGS += -DTEST
 
 $(SUBDIR)$(LIBNAME): $(OBJS)
 	$(RM) $@