Issue with Xcode/clang-900 and --enable-maintainer-mode

[Jim Jagielski <ji...@jaguNET.com>]

I just upgraded to Xcode 9, which installs clang-900[1].

I noticed that this now breaks several aspects of our configure
system when using --enable-maintainer-mode due to issues with
AC_CHECK_LIB. In particular, -Werror,-Wstrict-prototypes

Note for example, this error:

   configure:22140: checking for luaL_newstate in -llua
   configure:22165: gcc -o conftest -g -O0 -Wall -Wmissing-prototypes -Wstrict-prototypes -Wmissing-declarations -Wpointer-arith -std=c89 -Werror -Wdeclaration-afte
r-statement -Wformat -Wformat-security -Wunused  -DDARWIN -DSIGPROCMASK_SETS_THREAD_MASK -DDARWIN_10 -DAP_DEBUG -L/usr/local/lib   conftest.c -llua   >&5
   conftest.c:50:20: error: this function declaration is not a prototype [-Werror,-Wstrict-prototypes]
   char luaL_newstate ();
                      ^
                       void
   1 error generated.
   configure:22165: $? = 1


As can be seen, since AC_CHECK_LIB doesn't bother with function args, clang
errors out with this. THIS HAPPENS WITH ALL FUNCS SEARCHED FOR USING
AC_CHECK_LIB!

Anyway, why this never happened before is the big mystery.


1. cc -v
   Apple LLVM version 9.0.0 (clang-900.0.37)
   Target: x86_64-apple-darwin16.7.0
   Thread model: posix
   InstalledDir: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin