[gcc(refs/users/egallager/heads/autotools-tinkering)] improve error for when /usr/include isn't found

[gcc(refs/users/egallager/heads/autotools-tinkering)] improve error for when /usr/include isn't found

[Eric Gallager]

https://gcc.gnu.org/g:0f86c32611a55b15668aa82306d2d17a9b395432

commit 0f86c32611a55b15668aa82306d2d17a9b395432
Author: Eric Gallager <egallager@gcc.gnu.org>
Date:   Wed May 25 12:45:33 2022 -0400

    improve error for when /usr/include isn't found
    
    addresses PR90835

Diff:
---
 gcc/Makefile.in | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/gcc/Makefile.in b/gcc/Makefile.in
index 97e5450ecb5..535c475dfab 100644
--- a/gcc/Makefile.in
+++ b/gcc/Makefile.in
@@ -55,6 +55,7 @@ MAKEOVERRIDES =
 # -------------------------------
 
 build=@build@
+build_os=@build_os@
 host=@host@
 host_noncanonical=@host_noncanonical@
 host_os=@host_os@
@@ -3240,8 +3241,13 @@ stmp-fixinc: gsyslimits.h macro_list fixinc_list \
 	    multi_dir=`echo $${ml} | sed -e 's/^[^;]*;//'`; \
 	    fix_dir=include-fixed$${multi_dir}; \
 	    if ! $(inhibit_libc) && test ! -d ${BUILD_SYSTEM_HEADER_DIR}; then \
-	      echo The directory that should contain system headers does not exist: >&2 ; \
+	      echo "The directory (BUILD_SYSTEM_HEADER_DIR) that should contain system headers does not exist:" >&2 ; \
 	      echo "  ${BUILD_SYSTEM_HEADER_DIR}" >&2 ; \
+	      case ${build_os} in \
+	        darwin*) \
+	          echo "(on darwin this usually means you need to pass the --with-sysroot flag to configure to point it to where the system headers are actually put)" >&2; \
+	          ;; \
+	      esac; \
 	      tooldir_sysinc=`echo "${gcc_tooldir}/sys-include" | sed -e :a -e "s,[^/]*/\.\.\/,," -e ta`; \
 	      if test "x${BUILD_SYSTEM_HEADER_DIR}" = "x$${tooldir_sysinc}"; \
 	      then sleep 1; else exit 1; fi; \