Issues with posix functions on modern macOS/Xcode

[Martin Storsjö]

On Xcode 12.2 on macOS 11.0 on arm64, the following sequence fails to 
build:

$ ./gnulib-tool --create-testdir --dir=/tmp/testdir-posix \
               --single-configure --avoid=havelib-tests \
               `./posix-modules`
$ cd /tmp/testdir-posix
$ ./configure CPPFLAGS=-Wall 2>&1 | tee log1
$ make 2>&1 | tee log2
$ make check 2>&1 | tee log3


The "make" step fails with the following error:

gcc  -g -O2   -o test-dprintf-posix2 test-dprintf-posix2.o libtests.a 
../gllib/libgnu.a libtests.a ../gllib/libgnu.a libtests.a
Undefined symbols for architecture arm64:
  "_vm_region", referenced from:
      _vma_iterate in libtests.a(vma-iter.o)
ld: symbol(s) not found for architecture arm64


This same bit does succeed on x86_64 though - it looks like 
gnulib/lib/vma-iter.c has a macos specific arch check like this:

# if defined __ppc64__ || defined __x86_64__

This probably needs to be amended with "|| defined __aarch64__".

On macOS 10.15.7 (Catalina) on x86_64, both with Xcode 11.7 and 12.2, the 
following tests fail:

FAIL: test-dprintf-posix2.sh
FAIL: test-fflush2.sh
FAIL: test-fprintf-posix3.sh
FAIL: test-fpurge
FAIL: test-ftell.sh
FAIL: test-ftell2.sh
FAIL: test-ftello.sh
FAIL: test-ftello2.sh
FAIL: test-futimens
FAIL: test-renameat
FAIL: test-renameatu
FAIL: test-strsignal
FAIL: test-utime
FAIL: test-utimens
FAIL: test-utimensat

// Martin

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