Merge bitcoin/bitcoin#27798: depends: modernize clang flags for Darwin

cbee1d7091 depends: modernize clang flags (Cory Fields)
2a85857ce5 ci: disable false-positive warnings for now (Cory Fields)

Pull request description:

  This is a cleaner and simpler alternative to #25098. Inspired by [this conversation](https://github.com/bitcoin/bitcoin/pull/27737#issuecomment-1562543301). The diff is large but the change itself is quite small.

  Fixes builds with llvm >= 11 in guix by working around the problem. As a bonus, this is much cleaner and more maintainable than what we had before.

  See the updated comment for more info. At a high level: rather than playing tricks and trying to work around clang's default includes, disable them and re-add what we want.

ACKs for top commit:
  fanquake:
    ACK cbee1d7091 - tested Guix and the depends cross-compile. Would like to move this along, to unblock #27676, which itself might be a blocker for #27897. Note that macOS might seem somewhat in flux for the moment, but once we finish the migration to LLVM Clang + LLD, things will be must simpler, and ultimately more maintainable.
  TheCharlatan:
    ACK cbee1d7091

Tree-SHA512: 5a8300be528f550e15ab23d869e77df7a62201c6d40c0384795a9eecee38118a676e0b79b2b76c5e597597181443caada54a01b75a544dbcde76da1deba8e3a4

ci/test/00_setup_env_mac.sh

@@ -15,4 +15,7 @@ export XCODE_BUILD_ID=12B45b
 export RUN_UNIT_TESTS=false
 export RUN_FUNCTIONAL_TESTS=false
 export GOAL="deploy"
-export BITCOIN_CONFIG="--with-gui --enable-reduce-exports"
+
+# False-positive warning is fixed with clang 17, remove this when that version
+# can be used.
+export BITCOIN_CONFIG="--with-gui --enable-reduce-exports LDFLAGS=-Wno-error=unused-command-line-argument"