macos: try CMAKE_IGNORE_PREFIX_PATH

_build.sh

@@ -842,6 +842,7 @@ build_single_target() {
     # NOTE: 10.8 (and older) trigger C++ issues with Xcode and CMake.
     macminver='10.9'
     _CMAKE_GLOBAL+=" -DCMAKE_OSX_DEPLOYMENT_TARGET=${macminver}"
+    # FIXME: This option might have been renamed to `-mmacos-version-min=`?
     _CFLAGS_GLOBAL+=" -mmacosx-version-min=${macminver}"
     _CXXFLAGS_GLOBAL+=" -mmacosx-version-min=${macminver}"
     _OSVER="$(printf '%02d%02d' \
@@ -1185,8 +1186,10 @@ build_single_target() {
     # Minimum SDK version supported by Xcode releases:
     #   https://developer.apple.com/support/xcode/
 
-    # Explicitly set the SDK root. This forces clang to drop /usr/local
-    # from the list of default header search paths.
+    # Do not pick up components from this prefix:
+    _CMAKE_GLOBAL+=" -DCMAKE_IGNORE_PREFIX_PATH=${brew_root}"
+
+    # Explicitly set the SDK root.
     # We set it for all build tools for macOS to gain control over this.
     _SYSROOT="$(xcrun -sdk macosx --show-sdk-path)"  # E.g. /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk