build(xcode.mk): set default macOS build enviroment variables

set default values for envvars SDKROOT, MACOSX_DEPLOYMENT_TARGET if not set.
set CMAKE_OSX_ARCHITECTURES if building universal macOS binary.
these variables are used transparently in `make xcode/thirdparty`.

thirdparty.mk

@@ -33,7 +33,6 @@ capnproto:
 	-DBUILD_TESTING:BOOL=OFF \
 	-DCMAKE_BUILD_TYPE:STRING="Release" \
 	-DCMAKE_INSTALL_PREFIX:PATH="$(THIRD_PARTY_DIR)" \
-	$(CMAKE_OSX_ARCHS) \
 	&& cmake --build $(build) --target install
 
 glog:
@@ -43,7 +42,6 @@ glog:
 	-DWITH_GFLAGS:BOOL=OFF \
 	-DCMAKE_BUILD_TYPE:STRING="Release" \
 	-DCMAKE_INSTALL_PREFIX:PATH="$(THIRD_PARTY_DIR)" \
-	$(CMAKE_OSX_ARCHS) \
 	&& cmake --build $(build) --target install
 
 gtest:
@@ -52,7 +50,6 @@ gtest:
 	-DBUILD_GMOCK:BOOL=OFF \
 	-DCMAKE_BUILD_TYPE:STRING="Release" \
 	-DCMAKE_INSTALL_PREFIX:PATH="$(THIRD_PARTY_DIR)" \
-	$(CMAKE_OSX_ARCHS) \
 	&& cmake --build $(build) --target install
 
 leveldb:
@@ -62,15 +59,13 @@ leveldb:
 	-DLEVELDB_BUILD_TESTS:BOOL=OFF \
 	-DCMAKE_BUILD_TYPE:STRING="Release" \
 	-DCMAKE_INSTALL_PREFIX:PATH="$(THIRD_PARTY_DIR)" \
-	$(CMAKE_OSX_ARCHS) \
 	&& cmake --build $(build) --target install
 
 marisa:
 	cd $(SRC_DIR)/marisa-trie; \
 	cmake $(SRC_DIR) -B$(build) \
 	-DCMAKE_BUILD_TYPE:STRING="Release" \
 	-DCMAKE_INSTALL_PREFIX:PATH="$(THIRD_PARTY_DIR)" \
-	$(CMAKE_OSX_ARCHS) \
 	&& cmake --build $(build) --target install
 
 opencc:
@@ -79,7 +74,6 @@ opencc:
 	-DBUILD_SHARED_LIBS:BOOL=OFF \
 	-DCMAKE_BUILD_TYPE:STRING="Release" \
 	-DCMAKE_INSTALL_PREFIX:PATH="$(THIRD_PARTY_DIR)" \
-	$(CMAKE_OSX_ARCHS) \
 	&& cmake --build $(build) --target install
 
 yaml-cpp:
@@ -90,5 +84,4 @@ yaml-cpp:
 	-DYAML_CPP_BUILD_TOOLS:BOOL=OFF \
 	-DCMAKE_BUILD_TYPE:STRING="Release" \
 	-DCMAKE_INSTALL_PREFIX:PATH="$(THIRD_PARTY_DIR)" \
-	$(CMAKE_OSX_ARCHS) \
 	&& cmake --build $(build) --target install

xcode.mk

@@ -7,8 +7,15 @@ CMAKE_BOOST_OPTIONS = -DBoost_NO_BOOST_CMAKE=TRUE \
 	-DBOOST_ROOT="$(BOOST_ROOT)"
 endif
 
+# https://cmake.org/cmake/help/latest/variable/CMAKE_OSX_SYSROOT.html
+export SDKROOT ?= $(shell xcrun --sdk macosx --show-sdk-path)
+
+# https://cmake.org/cmake/help/latest/envvar/MACOSX_DEPLOYMENT_TARGET.html
+export MACOSX_DEPLOYMENT_TARGET ?= 10.9
+
 ifdef BUILD_UNIVERSAL
-export CMAKE_OSX_ARCHS = -DCMAKE_OSX_ARCHITECTURES="arm64;x86_64"
+# https://cmake.org/cmake/help/latest/envvar/CMAKE_OSX_ARCHITECTURES.html
+export CMAKE_OSX_ARCHITECTURES = arm64;x86_64
 endif
 
 ICU_PREFIX = $(shell brew --prefix)/opt/icu4c
@@ -26,8 +33,7 @@ release:
 	-DBUILD_STATIC=ON \
 	-DCMAKE_BUILD_WITH_INSTALL_RPATH=ON \
 	-DCMAKE_INSTALL_PREFIX="$(RIME_DIST_DIR)" \
-	$(CMAKE_BOOST_OPTIONS) \
-	$(CMAKE_OSX_ARCHS)
+	$(CMAKE_BOOST_OPTIONS)
 	cmake --build $(build) --config Release
 
 release-with-icu:
@@ -37,8 +43,7 @@ release-with-icu:
 	-DCMAKE_BUILD_WITH_INSTALL_RPATH=ON \
 	-DCMAKE_INSTALL_PREFIX="$(RIME_DIST_DIR)" \
 	-DCMAKE_PREFIX_PATH="$(ICU_PREFIX)" \
-	$(CMAKE_BOOST_OPTIONS) \
-	$(CMAKE_OSX_ARCHS)
+	$(CMAKE_BOOST_OPTIONS)
 	cmake --build $(build) --config Release
 
 debug: