Makefile: Compile zlib .c files with DMD via importC

As was already done in the former win{32,64}.mak files on Windows,
but not in posix.mak.

Makefile

@@ -101,59 +101,23 @@ else
  DRUNTIME = $(DRUNTIME_PATH)/../generated/$(OS)/$(BUILD)/$(MODEL)/druntime.lib
 endif
 
-# Set CC and DMD
+# Set DMD
 ifeq ($(OS),win32wine)
- CC = wine dmc.exe
  DMD = wine dmd.exe
  RUN = wine
 else
  DMD = $(DMD_DIR)/generated/$(OS)/$(BUILD)/$(MODEL)/dmd$(DOTEXE)
- ifeq ($(MODEL),32omf)
- CC = dmc
- else ifeq ($(OS),windows)
- CC = cl.exe
- else
- CC = cc
- endif
  RUN =
 endif
 
-# Set CFLAGS
-OUTFILEFLAG = -o
+# Set extra CFLAGS (for DMD - the zlib .c files are compiled via importC)
 NODEFAULTLIB=-defaultlib= -debuglib=
 ifeq (,$(findstring win,$(OS)))
- CFLAGS=$(MODEL_FLAG) -fPIC -std=c11 -DHAVE_UNISTD_H
+ CFLAGS += -P=-DHAVE_UNISTD_H
 # Bundled with the system library on OSX, and doesn't work with >= MacOS 11
  ifneq (osx,$(OS))
  NODEFAULTLIB += -L-lpthread -L-lm
  endif
- ifeq ($(BUILD),debug)
- CFLAGS += -g
- else
- CFLAGS += -O3
- endif
-else
- ifeq ($(MODEL),32omf)
- CFLAGS=-DNO_snprintf
- ifeq ($(BUILD),debug)
- CFLAGS += -g
- else
- CFLAGS += -O
- endif
- else # win64/win32coff
- OUTFILEFLAG = /Fo
- CFLAGS += /nologo /Zl /GS-
- ifeq ($(BUILD),debug)
- CFLAGS += /Z7
- else
- CFLAGS += /O2
- endif
- endif
-endif
-ifeq (osx,$(OS))
- ifeq (64,$(MODEL))
- CFLAGS+=--target=x86_64-darwin-apple # ARM cpu is not supported by dmd
- endif
 endif
 
 
@@ -351,8 +315,7 @@ lib: $(LIB)
 dll: $(ROOT)/libphobos2.so
 
 $(ROOT)/%$(DOTOBJ): %.c
- @[ -d $(dir $@) ] || mkdir -p $(dir $@) || [ -d $(dir $@) ]
- $(CC) -c $(CFLAGS) $< $(OUTFILEFLAG)$@
+ $(DMD) -c $(DFLAGS) -P=-Ietc/c/zlib $(CFLAGS) -of$@ $<
 
 $(LIB): $(OBJS) $(ALL_D_FILES) $(DRUNTIME)
  $(DMD) $(DFLAGS) -lib -of$@ $(DRUNTIME) $(D_FILES) $(OBJS)