depends: hard-code necessary c(xx)flags rather than setting them per-host

The per-host flag variables hold platform-specific defaults that are ignored
when flag environment variables are set, so it was wrong for them to contain
-std options relied on by package definitions.

Additionally, these flags (-pipe and -std=xx) will no longer be passed into
the CMake build, meaning less duplication in the build summary.

Pulled out of #31920.

depends/hosts/darwin.mk

@@ -60,8 +60,8 @@ darwin_CXX=$(clangxx_prog) --target=$(host) \
                -iwithsysroot/usr/include/c++/v1 \
                -iwithsysroot/usr/include -iframeworkwithsysroot/System/Library/Frameworks
 
-darwin_CFLAGS=-pipe -std=$(C_STANDARD) -mmacos-version-min=$(OSX_MIN_VERSION)
-darwin_CXXFLAGS=-pipe -std=$(CXX_STANDARD) -mmacos-version-min=$(OSX_MIN_VERSION)
+darwin_CFLAGS=-mmacos-version-min=$(OSX_MIN_VERSION)
+darwin_CXXFLAGS=-mmacos-version-min=$(OSX_MIN_VERSION)
 darwin_LDFLAGS=-Wl,-platform_version,macos,$(OSX_MIN_VERSION),$(OSX_SDK_VERSION)
 
 ifneq ($(build_os),darwin)