[Bug bootstrap/78251] config/gettext.m4 and config/iconv.m4 contaminate CPPFLAGS (can lead to build failures when libunwind-headers from MacPorts is active)

[michael+gcc at stapelberg dot ch]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78251

--- Comment #12 from Michael Stapelberg <michael+gcc at stapelberg dot ch> ---
I’m also running into this bug: I have recently started linking strace against
libunwind (for its handy --stack-traces option), and like having strace
available in my package build dependencies to debug build failures
interactively.

I’m using gcc 9.3.0 and libunwind 1.4.0. The first build failure message I’m
encountering is (I attached the full build log to this bug, too):

libtool: compile:  /usr/src/gcc-amd64-9.3.0-4/build/./gcc/xgcc -shared-libgcc
-B/usr/src/gcc-amd64-9.3.0-4/build/./gcc -nostdinc++
-L/usr/src/gcc-amd64-9.3.0-4/build/x86_64-pc-linux-gnu/libstdc++-v3/src
-L/usr/src/gcc-amd64-9.3.0-4/build/x86_64-pc-linux-gnu/libstdc++-v3/src/.libs
-L/usr/src/gcc-amd64-9.3.0-4/build/x86_64-pc-linux-gnu/libstdc++-v3/libsupc++/.libs
-B/ro/gcc-amd64-9.3.0-4/out/x86_64-pc-linux-gnu/bin/
-B/ro/gcc-amd64-9.3.0-4/out/x86_64-pc-linux-gnu/lib/ -isystem
/ro/gcc-amd64-9.3.0-4/out/x86_64-pc-linux-gnu/include -isystem
/ro/gcc-amd64-9.3.0-4/out/x86_64-pc-linux-gnu/sys-include -fno-checking
-I/usr/src/gcc-amd64-9.3.0-4/libstdc++-v3/../libgcc
-I/usr/src/gcc-amd64-9.3.0-4/build/x86_64-pc-linux-gnu/libstdc++-v3/include/x86_64-pc-linux-gnu
-I/usr/src/gcc-amd64-9.3.0-4/build/x86_64-pc-linux-gnu/libstdc++-v3/include
-I/usr/src/gcc-amd64-9.3.0-4/libstdc++-v3/libsupc++ -D_GLIBCXX_SHARED
-fno-implicit-templates -Wall -Wextra -Wwrite-strings -Wcast-qual -Wabi=2
-fdiagnostics-show-location=once -ffunction-sections -fdata-sections
-frandom-seed=eh_ptr.lo -g -O2 -D_GNU_SOURCE -c
/usr/src/gcc-amd64-9.3.0-4/libstdc++-v3/libsupc++/eh_ptr.cc  -fPIC -DPIC
-D_GLIBCXX_SHARED -o eh_ptr.o
libtool: compile:  /usr/src/gcc-amd64-9.3.0-4/build/./gcc/xgcc -shared-libgcc
-B/usr/src/gcc-amd64-9.3.0-4/build/./gcc -nostdinc++
-L/usr/src/gcc-amd64-9.3.0-4/build/x86_64-pc-linux-gnu/libstdc++-v3/src
-L/usr/src/gcc-amd64-9.3.0-4/build/x86_64-pc-linux-gnu/libstdc++-v3/src/.libs
-L/usr/src/gcc-amd64-9.3.0-4/build/x86_64-pc-linux-gnu/libstdc++-v3/libsupc++/.libs
-B/ro/gcc-amd64-9.3.0-4/out/x86_64-pc-linux-gnu/bin/
-B/ro/gcc-amd64-9.3.0-4/out/x86_64-pc-linux-gnu/lib/ -isystem
/ro/gcc-amd64-9.3.0-4/out/x86_64-pc-linux-gnu/include -isystem
/ro/gcc-amd64-9.3.0-4/out/x86_64-pc-linux-gnu/sys-include -fno-checking
-I/usr/src/gcc-amd64-9.3.0-4/libstdc++-v3/../libgcc
-I/usr/src/gcc-amd64-9.3.0-4/build/x86_64-pc-linux-gnu/libstdc++-v3/include/x86_64-pc-linux-gnu
-I/usr/src/gcc-amd64-9.3.0-4/build/x86_64-pc-linux-gnu/libstdc++-v3/include
-I/usr/src/gcc-amd64-9.3.0-4/libstdc++-v3/libsupc++ -D_GLIBCXX_SHARED
-fno-implicit-templates -Wall -Wextra -Wwrite-strings -Wcast-qual -Wabi=2
-fdiagnostics-show-location=once -ffunction-sections -fdata-sections
-frandom-seed=eh_personality.lo -g -O2 -D_GNU_SOURCE -c
/usr/src/gcc-amd64-9.3.0-4/libstdc++-v3/libsupc++/eh_personality.cc  -fPIC
-DPIC -D_GLIBCXX_SHARED -o eh_personality.o
In file included from
/usr/src/gcc-amd64-9.3.0-4/libstdc++-v3/libsupc++/eh_call.cc:28:
/usr/src/gcc-amd64-9.3.0-4/libstdc++-v3/libsupc++/unwind-cxx.h:92:3: error:
'_Unwind_Ptr' does not name a type; did you mean '_Unwind_SetIP'?
   92 |   _Unwind_Ptr catchTemp;
      |   ^~~~~~~~~~~
      |   _Unwind_SetIP
/usr/src/gcc-amd64-9.3.0-4/libstdc++-v3/libsupc++/unwind-cxx.h:146:3: error:
'_Unwind_Ptr' does not name a type; did you mean '_Unwind_SetIP'?
  146 |   _Unwind_Ptr catchTemp;
      |   ^~~~~~~~~~~
      |   _Unwind_SetIP