ci: disable false-positive warnings for now

clang <=17 warns on -nostdlibinc, which causes an error on our -Werror builds.

Note that this breaks the "-fPIE" check in configure because it relies on
catching warnings, but that is not a problem for macOS.

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"