os/board/rtl8730e: Optimize the CFLAGS length

Generate a response file containing all the CFLAGS instead of loading an entire CFLAGS string directly.

---

> Before
CFLAGS length: 3777 / 4096

> After
CFLAGS length: 28 / 4096

Built with both configurations (flat apps), MD5 sum of TizenRT/build/output/bin/kernel_rtl8730e_200204.trpk match.

Author: EangJS

os/board/rtl8730e/src/Makefile

@@ -218,6 +218,11 @@ else
 
 endif
 
+# Generate response file containing all CFLAGS
+CFLAGS_FILE := $(TOPDIR)/cflags.rsp
+$(shell printf "%s" "$(CFLAGS)" > $(CFLAGS_FILE))
+CFLAGS := @$(CFLAGS_FILE)
+
 all: libboard$(LIBEXT)
 
 $(AOBJS): %$(OBJEXT): %$(ASMEXT)