Merge branch 'jk/use-wunreachable-code-for-devs'

Enable -Wunreachable-code for developer builds.

* jk/use-wunreachable-code-for-devs:
  config.mak.dev: enable -Wunreachable-code
  git-compat-util: add NOT_CONSTANT macro and use it in atfork_prepare()
  run-command: use errno to check for sigfillset() error

meson.build

@@ -264,6 +264,7 @@ libgit_sources = [
   'compat/nonblock.c',
   'compat/obstack.c',
   'compat/terminal.c',
+  'compiler-tricks/not-constant.c',
   'config.c',
   'connect.c',
   'connected.c',
@@ -719,6 +720,7 @@ if get_option('warning_level') in ['2','3', 'everything'] and compiler.get_argum
     '-Woverflow',
     '-Wpointer-arith',
     '-Wstrict-prototypes',
+    '-Wunreachable-code',
     '-Wunused',
     '-Wvla',
     '-Wwrite-strings',