bug#30700: 27.0.50; Broken tests on macOS

[Philipp]

The following tests fail for me on macOS with a recent master build:

network-stream-tests:

Test echo-server-with-dns backtrace:
  make-network-process(:name "server" :server t :noquery t :family ipv
  make-server("p")
  (let* ((server (make-server (system-name))) (port (aref (process-con
  (closure (t) nil (let* ((server (make-server (system-name))) (port (
  ert--run-test-internal(#s(ert--test-execution-info :test #s(ert-test
  ert-run-test(#s(ert-test :name echo-server-with-dns :documentation n
  ert-run-or-rerun-test(#s(ert--stats :selector (not (or (tag :expensi
  ert-run-tests((not (or (tag :expensive-test) (tag :unstable))) #f(co
  ert-run-tests-batch((not (or (tag :expensive-test) (tag :unstable)))
  ert-run-tests-batch-and-exit((not (or (tag :expensive-test) (tag :un
  eval((ert-run-tests-batch-and-exit '(not (or (tag :expensive-test) (
  command-line-1(("-L" ":." "-l" "ert" "-l" "lisp/net/network-stream-t
  command-line()
  normal-top-level()
Test echo-server-with-dns condition:
    (error "p/0 nodename nor servname provided, or not known")

The macOS firewall prevents creating the server here.  Probably we
should just skip this test on macOS.


flymake-tests:

3 unexpected results:
   FAILED  included-c-header-files
   FAILED  warning-predicate-function-gcc
   FAILED  warning-predicate-rx-gcc

These tests fail because they seem to invoke GCC, and on macOS GCC is
actually Clang, so the output format is different from what's expected.
I'd suggest two fixes:

1. Instead of invoking GCC, save GCC's output once in a checked-in file.
   That makes the test more robust and reproducible because it no longer
   depends on the behavior of external programs.

2. Make Flymake work with the Clang output, i.e. remove the hard
   dependency on GCC.


In GNU Emacs 27.0.50 (build 57, x86_64-apple-darwin17.4.0, NS appkit-1561.20 
Version 10.13.3 (Build 17D102))
 of 2018-03-02 built on p
Repository revision: e58f9a45d6a31be4ca379e10a866766e0993f49e
Windowing system distributor 'Apple', version 10.3.1561
System Description:  Mac OS X 10.13.3

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.

Configured using:
 'configure --with-modules --without-pop --with-mailutils
 --enable-gcc-warnings=yes --enable-checking
 --enable-check-lisp-object-type 'CFLAGS=-ggdb3 -O0''

Configured features:
NOTIFY ACL GNUTLS LIBXML2 ZLIB TOOLKIT_SCROLL_BARS NS MODULES THREADS
JSON

Important settings:
  value of $LANG: de_DE.UTF-8
  locale-coding-system: utf-8-unix

Major mode: Lisp Interaction

Minor modes in effect:
  tooltip-mode: t
  global-eldoc-mode: t
  eldoc-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
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  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t
  transient-mark-mode: t

Load-path shadows:
None found.

Features:
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Memory information:
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 (symbols 48 20096 1)
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 (strings 32 28897 1948)
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