pkg/54684: lang/gcc48 won't build on macOS 10.15

[gson%gson.org@localhost (Andreas Gustafsson)]

>Number:         54684
>Category:       pkg
>Synopsis:       lang/gcc48 won't build on macOS 10.15
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    pkg-manager
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Fri Nov 08 15:00:00 +0000 2019
>Originator:     Andreas Gustafsson
>Release:        pkgsrc-current
>Organization:
>Environment:
System: macOS 10.15
Architecture: x86_64
Machine: amd64
>Description:

Building lang/gcc48 on macOS 10.15 (aka Catalina) fails with:

  libtool: compile:  /Users/gson/pkgsrc/lang/gcc48/work/build/./gcc/xgcc -shared-libgcc -B/Users/gson/pkgsrc/lang/gcc48/work/build/./gcc -nostdinc++ -L/Users/gson/pkgsrc/lang/gcc48/work/build/x86_64-apple-darwin19/libstdc++-v3/src -L/Users/gson/pkgsrc/lang/gcc48/work/build/x86_64-apple-darwin19/libstdc++-v3/src/.libs -B/Users/gson/pkg/gcc48/x86_64-apple-darwin19/bin/ -B/Users/gson/pkg/gcc48/x86_64-apple-darwin19/lib/ -isystem /Users/gson/pkg/gcc48/x86_64-apple-darwin19/include -isystem /Users/gson/pkg/gcc48/x86_64-apple-darwin19/sys-include -I/Users/gson/pkgsrc/lang/gcc48/work/gcc-4.8.5/libstdc++-v3/../libgcc -I/Users/gson/pkgsrc/lang/gcc48/work/build/x86_64-apple-darwin19/libstdc++-v3/include/x86_64-apple-darwin19 -I/Users/gson/pkgsrc/lang/gcc48/work/build/x86_64-apple-darwin19/libstdc++-v3/include -I/Users/gson/pkgsrc/lang/gcc48/work/gcc-4.8.5/libstdc++-v3/libsupc++ -D_GLIBCXX_SHARED -Wall -Wextra -Wwrite-strings -Wcast-qual -Wabi -fdiagnostics-show-location=once -fvisibility-inlin
 es-hidden -ffunction-sections -fdata-sections -frandom-seed=atexit_thread.lo -g -O2 -I/Users/gson/pkg/include -std=gnu++0x -c ../../../../gcc-4.8.5/libstdc++-v3/libsupc++/atexit_thread.cc  -fno-common -DPIC -D_GLIBCXX_SHARED -o atexit_thread.o
  In file included from /Users/gson/pkgsrc/lang/gcc48/work/build/gcc/include-fixed/Availability.h:273:0,
                   from /Users/gson/pkgsrc/lang/gcc48/work/build/gcc/include-fixed/stdlib.h:76,
                   from /Users/gson/pkgsrc/lang/gcc48/work/build/x86_64-apple-darwin19/libstdc++-v3/include/cstdlib:72,
                   from ../../../../gcc-4.8.5/libstdc++-v3/libsupc++/atexit_thread.cc:25:
  /Users/gson/pkgsrc/lang/gcc48/work/build/gcc/include-fixed/AvailabilityInternal.h:60:18: error: missing binary operator before token "("
   #if __has_include(<AvailabilityInternalPrivate.h>)
                    ^
  In file included from /Users/gson/pkgsrc/lang/gcc48/work/build/gcc/include-fixed/stdlib.h:76:0,
                   from /Users/gson/pkgsrc/lang/gcc48/work/build/x86_64-apple-darwin19/libstdc++-v3/include/cstdlib:72,
                   from ../../../../gcc-4.8.5/libstdc++-v3/libsupc++/atexit_thread.cc:25:
  /Users/gson/pkgsrc/lang/gcc48/work/build/gcc/include-fixed/Availability.h:595:18: error: missing binary operator before token "("
   #if __has_include(<AvailabilityProhibitedInternal.h>)
                    ^

>How-To-Repeat:

>Fix: