meson: suppress clang's -Watomic-alignment warnings on x86_64 (#76)

Running `./dev build` on x86_64 with Clang would by default [1][2]
produce about 2200 lines of -Watomic-alignment warnings, like:

    ../src/hatrack/hash/crown.c:416:25: warning: large atomic operation may incur significant performance penalty; the access size (16 bytes) exceeds the max lock-free size (8  bytes) [-Watomic-alignment]
      416 |         record        = atomic_read(&cur->record);
          |                         ^
    ../include/hatrack/hatomic.h:35:24: note: expanded from macro 'atomic_read'
       35 | #define atomic_read(x) atomic_load_explicit(x, memory_order_relaxed)
          |                        ^
    /usr/lib/clang/17/include/stdatomic.h:141:30: note: expanded from macro 'atomic_load_explicit'
      141 | #define atomic_load_explicit __c11_atomic_load
          |                              ^

But it's intentional that we use the emulation where it's not supported
in hardware. Suppress those warnings.

Closes: #68

[1] https://releases.llvm.org/7.0.0/tools/clang/docs/DiagnosticsReference.html#watomic-alignment
[2] https://releases.llvm.org/18.1.8/tools/clang/docs/DiagnosticsReference.html#watomic-alignment

meson.build

@@ -29,6 +29,10 @@ c_args        = ['-Wextra',
                   '-fno-omit-frame-pointer',
                   ]
 
+if (host_machine.cpu_family() == 'x86_64' and cc.get_id() == 'clang')
+  c_args    = c_args + ['-Wno-atomic-alignment']
+endif
+
 if (host_machine.system() == 'darwin')
   using_osx  = true
   link_args  = ['-target',