Revert "sim: Specify -fshort-wchar as NuttX wchar_t is 16-bit"

It's better to apply the default compiler option to improve the compatibility
This reverts commit 3fc06ff2d1.

boards/sim/sim/sim/scripts/Make.defs

@@ -95,16 +95,11 @@ NM = $(CROSSDEV)nm
 OBJCOPY = $(CROSSDEV)objcopy
 OBJDUMP = $(CROSSDEV)objdump
 
-# Note: -fshort-wchar for the case where NuttX and the host OS have
-# different wchar_t. On NuttX, it's uint16_t. On macOS, it's 32-bit.
 CFLAGS := $(ARCHWARNINGS) $(ARCHOPTIMIZATION) \
-   $(ARCHCPUFLAGS) $(ARCHINCLUDES) $(ARCHDEFINES) $(EXTRAFLAGS) -pipe \
-   -fshort-wchar
+   $(ARCHCPUFLAGS) $(ARCHINCLUDES) $(ARCHDEFINES) $(EXTRAFLAGS) -pipe
 CXXFLAGS := $(ARCHWARNINGSXX) $(ARCHOPTIMIZATION) \
-   $(ARCHCPUFLAGSXX) $(ARCHXXINCLUDES) $(ARCHDEFINES) $(EXTRAFLAGS) -pipe \
-   -fshort-wchar
-CPPFLAGS := $(ARCHINCLUDES) $(ARCHDEFINES) $(EXTRAFLAGS) \
-   -fshort-wchar
+   $(ARCHCPUFLAGSXX) $(ARCHXXINCLUDES) $(ARCHDEFINES) $(EXTRAFLAGS) -pipe
+CPPFLAGS := $(ARCHINCLUDES) $(ARCHDEFINES) $(EXTRAFLAGS)
 AFLAGS := $(CFLAGS) -D__ASSEMBLY__
 
 ifeq ($(CONFIG_LIBCXX),y)