toolchain/56128: NetBSD 9 release branch will not cross-build on Darwin

[cjep%netbsd.org@localhost]

>Number:         56128
>Category:       toolchain
>Synopsis:       NetBSD 9 release branch will not cross-build on Darwin
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    toolchain-manager
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sun Apr 25 12:55:00 +0000 2021
>Originator:     Chris Pinnock
>Release:        NetBSD 9.1_STABLE
>Organization:
>Environment:
Darwin MacMini-7390 20.3.0 Darwin Kernel Version 20.3.0: Thu Jan 21 00:07:06 PST 2021; root:xnu-7195.81.3~1/RELEASE_X86_64 x86_64
Latest NetBSD 9 branch. Attempting to build.sh on amd64, i386, sun2 and others.

>Description:

The cross-build on Darwin fails as follows:

--- xexit.o ---
/Volumes/TimeMachine/Chris/NetBSD/NetBSD9/src/tools/texinfo/../../external/gpl2/texinfo/dist/lib/xexit.c:67:3: error: implicitly declaring library function 'exit' with type 'void (int) __attribute__((noreturn))' [-Werror,-Wimplicit-function-declaration]
  exit (exit_status);
  ^
/Volumes/TimeMachine/Chris/NetBSD/NetBSD9/src/tools/texinfo/../../external/gpl2/texinfo/dist/lib/xexit.c:67:3: note: include the header <stdlib.h> or explicitly provide a declaration for 'exit'
--- xmalloc.o ---
/Volumes/TimeMachine/Chris/NetBSD/NetBSD9/src/tools/texinfo/../../external/gpl2/texinfo/dist/lib/xmalloc.c:31:3: error: implicitly declaring library function 'abort' with type 'void (void) __attribute__((noreturn))' [-Werror,-Wimplicit-function-declaration]
  abort ();
  ^
/Volumes/TimeMachine/Chris/NetBSD/NetBSD9/src/tools/texinfo/../../external/gpl2/texinfo/dist/lib/xmalloc.c:31:3: note: include the header <stdlib.h> or explicitly provide a declaration for 'abort'
/Volumes/TimeMachine/Chris/NetBSD/NetBSD9/src/tools/texinfo/../../external/gpl2/texinfo/dist/lib/xmalloc.c:40:16: error: implicitly declaring library function 'malloc' with type 'void *(unsigned long)' [-Werror,-Wimplicit-function-declaration]
  void *temp = malloc (bytes);
               ^
/Volumes/TimeMachine/Chris/NetBSD/NetBSD9/src/tools/texinfo/../../external/gpl2/texinfo/dist/lib/xmalloc.c:40:16: note: include the header <stdlib.h> or explicitly provide a declaration for 'malloc'
/Volumes/TimeMachine/Chris/NetBSD/NetBSD9/src/tools/texinfo/../../external/gpl2/texinfo/dist/lib/xmalloc.c:55:12: error: implicitly declaring library function 'realloc' with type 'void *(void *, unsigned long)' [-Werror,-Wimplicit-function-declaration]
    temp = realloc (pointer, bytes);
           ^
/Volumes/TimeMachine/Chris/NetBSD/NetBSD9/src/tools/texinfo/../../external/gpl2/texinfo/dist/lib/xmalloc.c:55:12: note: include the header <stdlib.h> or explicitly provide a declaration for 'realloc'
--- xexit.o ---
1 error generated.
--- xmalloc.o ---
3 errors generated.

nbmake[10]: stopped in /Volumes/TimeMachine/Chris/NetBSD/NetBSD9/obj/sun2-m68000/Volumes/TimeMachine/Chris/NetBSD/NetBSD9/src/tools/texinfo/build/lib

>How-To-Repeat:
	On Big Sur (latest), get recent NetBSD 9 branch sources
	./build.sh -U -m amd64 release
>Fix: