Remove MACOSX_DEPLOYMENT_TARGET in FFI Makefile

* Reapplies 9c5932f
* It causes `ld: library not found for -lgcc_s.10.4` in CI on Mojave.
* Add -Wno-unused-parameter to silence warnings.
* Do not try to compile 32-bit as that is warned:
  ld: warning: The i386 architecture is deprecated for macOS (remove from the Xcode build setting: ARCHS)

Author: eregon

spec/ffi/fixtures/GNUmakefile

@@ -23,8 +23,6 @@ PREFIX = lib
 LIBEXT ?= so
 LIBNAME = $(PREFIX)test.$(LIBEXT)
 
-export MACOSX_DEPLOYMENT_TARGET=10.4
-
 CCACHE := $(strip $(realpath $(shell which ccache 2> /dev/null)))
 
 TEST_SRCS = $(wildcard $(SRC_DIR)/*.c)
@@ -35,7 +33,7 @@ TEST_OBJS := $(patsubst $(SRC_DIR)/%.c, $(TEST_BUILD_DIR)/%.o, $(TEST_SRCS))
 #   http://weblogs.java.net/blog/kellyohair/archive/2006/01/compilation_of_1.html
 JFLAGS = -fno-omit-frame-pointer -fno-strict-aliasing
 OFLAGS = -O2 $(JFLAGS)
-WFLAGS = -W -Wall -Wno-unused -Wno-parentheses
+WFLAGS = -W -Wall -Wno-unused -Wno-unused-parameter -Wno-parentheses
 PICFLAGS = -fPIC
 SOFLAGS = -shared
 LDFLAGS += $(SOFLAGS)
@@ -58,9 +56,6 @@ ifeq ($(OS), darwin)
   ifneq ($(findstring $(CPU),ppc),)
     ARCHFLAGS += -arch ppc
   endif
-  ifneq ($(findstring $(CPU),i386 x86_64),)
-    ARCHFLAGS += -arch i386 -arch x86_64
-  endif
   CFLAGS += $(ARCHFLAGS) -DTARGET_RT_MAC_CFM=0
   CFLAGS += -fno-common
   LDFLAGS = $(ARCHFLAGS) -dynamiclib