It does seem to be gcc:

(snippet from output of 'make V=1' when compiling src/nsterm.m):
gcc -std=gnu99 -c -Demacs -I. -I. -I../lib -I../lib -D_REENTRANT -I
[...]  -MMD -MF deps/nsterm.d -MP -O0 -g3 nsterm.m


And IIRC 'gcc' is symlinked to 'clang' on later macOS versions.


On 18/07/2017 08:06, Anders Lindgren wrote:
> Hi Charles, thanks for replying!
>
> Yes, that is what I saw as well. The question is which compiler is 
> used (by default) when building Emacs on 10.6. I guess it is "gcc", 
> but I didn't have time to verify this.
>
>     -- Anders
>
> On Mon, Jul 17, 2017 at 10:09 PM, Charles A. Roelli <charles@aurox.ch 
> <mailto:charles@aurox.ch>> wrote:
>
>     clang and gcc seem different on 10.6 (can't say for certain, though):
>
>
>     $ which gcc
>     /usr/bin/gcc
>     $ gcc --version
>     i686-apple-darwin10-llvm-gcc-4.2 (GCC) 4.2.1 (Based on Apple Inc.
>     build 5658) (LLVM build 2335.15.00)
>     Copyright (C) 2007 Free Software Foundation, Inc.
>     This is free software; see the source for copying conditions.
>     There is NO
>     warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR
>     PURPOSE.
>
>     $ which clang
>     /usr/bin/clang
>     $ clang --version
>     Apple clang version 2.1 (tags/Apple/clang-163.7.1) (based on LLVM
>     3.0svn)
>     Target: x86_64-apple-darwin10.8.0
>     Thread model: posix
>
>
>
>
>
>     On 17/07/2017 01:01, Alan Third wrote:
>
>         On Sun, Jul 16, 2017 at 08:43:25PM +0200, Anders Lindgren wrote:
>
>             I tried to figure out if gcc or clang was used when
>             building on 10.6.8, but
>             ran out of time (and won't have the chance to do it again
>             anytime soon). I
>             did conclude that it comes with both a real "gcc" and a
>             real "clang", so
>             presumably gcc is used. (Surprisingly, more modern
>             versions of macOS seems
>             to map the command "gcc" to "clang".)
>
>         Charles can maybe answer this for us, as he uses 10.6.
>
>             A warning-free build is a must on modern system (which use
>             clang). It would
>             be nice on older system, I guess, but it would be hard to
>             enforce. (We
>             could even lobby to add the option to future gcc versions,
>             for the benefit
>             of GNUStep, but it would not help the situation on older
>             macOS versions.)
>             My gut feeling is to go with the
>             NS_SILENCE_MISSING_METHOD_WARNING_BEGIN
>             solution, as it work on modern macOS systems, it retains
>             type checking, and
>             it give us a single location to describe the situation and
>             to modify the
>             macro, if there should be a need for it in the future.
>
>         Agreed.
>
>         I think that a lot (if not most) of the code that we might
>         want to use
>         this on won’t work on GNUstep at all, so we could still exclude it
>         from building there if the warnings are too much.
>
>
>