Merge bitcoin/bitcoin#27721: depends: remove redundant stdlib option

4fe5f3c467 depends: remove redundant stdlib option (Cory Fields)

Pull request description:

  Like #27628, this is another dependency of #21778, though it doesn't become obvious until used with a newer clang.

  This should be a no-op.

  Use of -stdlib++-isystem gets rid of any system c++ header include paths and negates the need for this option. In newer versions of clangs the combo produces an annoying warning that actually causes problems during configure.

ACKs for top commit:
  fanquake:
    ACK 4fe5f3c467

Tree-SHA512: 904072f2b13dffbbeab2bc9ff20a74969888502fa1ea35d9030784dd397c6751e31233e6ec7dc34e9fd42574950be733b25d6653c2a93e214cc5e4eef2e0133a

depends/hosts/darwin.mk

@@ -63,7 +63,7 @@ $(foreach TOOL,$(cctools_TOOLS),$(eval darwin_$(TOOL) = $$(build_prefix)/bin/$$(
 #         Explicitly point to our binaries (e.g. cctools) so that they are
 #         ensured to be found and preferred over other possibilities.
 #
-#     -stdlib=libc++ -stdlib++-isystem$(OSX_SDK)/usr/include/c++/v1
+#     -stdlib++-isystem$(OSX_SDK)/usr/include/c++/v1
 #
 #         Forces clang to use the libc++ headers from our SDK and completely
 #         forget about the libc++ headers from the standard directories
@@ -107,7 +107,6 @@ darwin_CXX=env -u C_INCLUDE_PATH -u CPLUS_INCLUDE_PATH \
              $(clangxx_prog) --target=$(host) -mmacosx-version-min=$(OSX_MIN_VERSION) \
                -B$(build_prefix)/bin -mlinker-version=$(LD64_VERSION) \
                -isysroot$(OSX_SDK) \
-               -stdlib=libc++ \
                -stdlib++-isystem$(OSX_SDK)/usr/include/c++/v1 \
                -Xclang -internal-externc-isystem -Xclang $(clang_resource_dir)/include \
                -Xclang -internal-externc-isystem -Xclang $(OSX_SDK)/usr/include