Update warnings.cmake

AppleClang complains about missing braces as
```
[ 50%] Building CXX object test/cib/CMakeFiles/cib_nexus_test.dir/nexus.cpp.o
cd "build/Clang 16.0.0 arm64-apple-darwin24.1.0/test/cib" && /usr/bin/clang++ -DFMT_HEADER_ONLY=1 -Iinclude -isystem "build/Clang 16.0.0 arm64-apple-darwin24.1.0/_deps/catch2-src/src/catch2/.." -isystem "build/Clang 16.0.0 arm64-apple-darwin24.1.0/_deps/catch2-build/generated-includes" -isystem "build/Clang 16.0.0 arm64-apple-darwin24.1.0/_deps/rapidcheck-src/include" -isystem "build/Clang 16.0.0 arm64-apple-darwin24.1.0/_deps/rapidcheck-src/extras/catch/include" -isystem "build/Clang 16.0.0 arm64-apple-darwin24.1.0/_deps/mp11-src/include" -isystem "build/Clang 16.0.0 arm64-apple-darwin24.1.0/_deps/cpp-baremetal-concurrency-src/include" -isystem "build/Clang 16.0.0 arm64-apple-darwin24.1.0/_deps/fmt-src/include" -isystem "build/Clang 16.0.0 arm64-apple-darwin24.1.0/_deps/cpp-std-extensions-src/include" -isystem "build/Clang 16.0.0 arm64-apple-darwin24.1.0/_deps/cpp-baremetal-senders-and-receivers-src/include" -g -std=gnu++20 -arch arm64 -isysroot /Library/Developer/CommandLineTools/SDKs/MacOSX15.1.sdk -Wall -Wcast-align -Wconversion -Wdouble-promotion -Werror -Wextra -Wextra-semi -Wfatal-errors -Wformat=2 -Wold-style-cast -Woverloaded-virtual -Wshadow -Wunused -MD -MT test/cib/CMakeFiles/cib_nexus_test.dir/nexus.cpp.o -MF CMakeFiles/cib_nexus_test.dir/nexus.cpp.o.d -o CMakeFiles/cib_nexus_test.dir/nexus.cpp.o -c test/cib/nexus.cpp
In file included from test/cib/nexus.cpp:1:
In file included from include/cib/cib.hpp:40:
In file included from include/cib/config.hpp:5:
include/cib/detail/config_details.hpp:20:25: fatal error: suggest braces around initialization of subobject [-Wmissing-braces]
   20 |         : configs_tuple{configs...} {}
      |                         ^~~~~~~
      |                         {      }
include/cib/config.hpp:30:12: note: in instantiation of member function 'cib::detail::config<cib::detail::exports<TestCallback<0>>, cib::detail::extend<TestCallback<0>, SimpleConfig::(lambda at test/cib/nexus.cpp:22:38)>>::config' requested here
   30 |     return detail::config{configs...};
      |            ^
test/cib/nexus.cpp:20:41: note: in instantiation of function template specialization 'cib::config<cib::detail::exports<TestCallback<0>>, cib::detail::extend<TestCallback<0>, SimpleConfig::(lambda at test/cib/nexus.cpp:22:38)>>' requested here
   20 |     constexpr static auto config = cib::config(
      |                                         ^
1 error generated.
```

with the change compilation passes
```
[ 50%] Building CXX object test/cib/CMakeFiles/cib_nexus_test.dir/nexus.cpp.o
cd "build/Clang 16.0.0 arm64-apple-darwin24.1.0/test/cib" && /usr/bin/clang++ -DFMT_HEADER_ONLY=1 -Iinclude -isystem "build/Clang 16.0.0 arm64-apple-darwin24.1.0/_deps/catch2-src/src/catch2/.." -isystem "build/Clang 16.0.0 arm64-apple-darwin24.1.0/_deps/catch2-build/generated-includes" -isystem "build/Clang 16.0.0 arm64-apple-darwin24.1.0/_deps/rapidcheck-src/include" -isystem "build/Clang 16.0.0 arm64-apple-darwin24.1.0/_deps/rapidcheck-src/extras/catch/include" -isystem "build/Clang 16.0.0 arm64-apple-darwin24.1.0/_deps/mp11-src/include" -isystem "build/Clang 16.0.0 arm64-apple-darwin24.1.0/_deps/cpp-baremetal-concurrency-src/include" -isystem "build/Clang 16.0.0 arm64-apple-darwin24.1.0/_deps/fmt-src/include" -isystem "build/Clang 16.0.0 arm64-apple-darwin24.1.0/_deps/cpp-std-extensions-src/include" -isystem "build/Clang 16.0.0 arm64-apple-darwin24.1.0/_deps/cpp-baremetal-senders-and-receivers-src/include" -g -std=gnu++20 -arch arm64 -isysroot /Library/Developer/CommandLineTools/SDKs/MacOSX15.1.sdk -Wall -Wcast-align -Wconversion -Wdouble-promotion -Werror -Wextra -Wextra-semi -Wfatal-errors -Wformat=2 -Wold-style-cast -Woverloaded-virtual -Wshadow -Wunused -Wno-missing-braces -MD -MT test/cib/CMakeFiles/cib_nexus_test.dir/nexus.cpp.o -MF CMakeFiles/cib_nexus_test.dir/nexus.cpp.o.d -o CMakeFiles/cib_nexus_test.dir/nexus.cpp.o -c test/cib/nexus.cpp
```

@elbeno related PR intel/compile-time-init-build#651

Author: oxidase

cmake/warnings.cmake

@@ -30,4 +30,6 @@ target_compile_options(
         $<$<CXX_COMPILER_ID:Clang>:-Wshift-sign-overflow>
         $<$<CXX_COMPILER_ID:GNU>:-Wuseless-cast>
         -Wunused
-        $<$<CXX_COMPILER_ID:Clang>:-Wmissing-prototypes>)
+        $<$<CXX_COMPILER_ID:Clang>:-Wmissing-prototypes>
+        $<$<CXX_COMPILER_ID:AppleClang>:-Wno-missing-braces>)
+