[Bug bootstrap/89864] [9 regression] gcc fails to build/bootstrap with XCode 10.2

[juergen.reuter at desy dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89864

--- Comment #56 from Jürgen Reuter <juergen.reuter at desy dot de> ---
I tried the fix, but now I get another error:
/libstdc++-v3/../libgcc
-I/usr/local/packages/gcc_9.0_fixincl/_build/x86_64-apple-darwin18.5.0/i386/libstdc++-v3/include/x86_64-apple-darwin18.5.0
-I/usr/local/packages/gcc_9.0_fixincl/_build/x86_64-apple-darwin18.5.0/i386/libstdc++-v3/include
-I/usr/local/packages/gcc_9.0_fixincl/libstdc++-v3/libsupc++ -std=gnu++17
-D_GLIBCXX_SHARED -fno-implicit-templates -Wall -Wextra -Wwrite-strings
-Wcast-qual -Wabi=2 -fdiagnostics-show-location=once -ffunction-sections
-fdata-sections -frandom-seed=fs_dir.lo -fimplicit-templates -g -O2 -m32 -c
../../../../../../libstdc++-v3/src/c++17/fs_dir.cc  -fno-common -DPIC
-D_GLIBCXX_SHARED -o fs_dir.o
../../../../../../libstdc++-v3/src/c++17/fs_ops.cc:31:10: fatal error:
filesystem: No such file or directory
   31 | #include <filesystem>
      |          ^~~~~~~~~~~~
compilation terminated.