llama : remove apple-a12 flag for ios-sim and ios-device builds

This commit removes the -mcpu=apple-a12 flag from the ios-sim and
ios-device builds. This should not be required now that we are setting
GGML_NATIVE=OFF.

The motivation for this is that these flags were causing the following
error when building the xcframework:
```console
    clang: error: unsupported option '-mcpu=' for target 'x86_64-apple-ios16.4-simulator'
```

Author: danbev

build-xcframework.sh

@@ -139,8 +139,8 @@ cmake -B build-ios-sim -G Xcode \
     -DCMAKE_OSX_SYSROOT=iphonesimulator \
     -DCMAKE_OSX_ARCHITECTURES="arm64;x86_64" \
     -DCMAKE_XCODE_ATTRIBUTE_SUPPORTED_PLATFORMS=iphonesimulator \
-    -DCMAKE_C_FLAGS="-mcpu=apple-a12 ${COMMON_C_FLAGS}" \
-    -DCMAKE_CXX_FLAGS="-mcpu=apple-a12 ${COMMON_CXX_FLAGS}" \
+    -DCMAKE_C_FLAGS="${COMMON_C_FLAGS}" \
+    -DCMAKE_CXX_FLAGS="${COMMON_CXX_FLAGS}" \
     -S .
 cmake --build build-ios-sim --config Release -- -quiet
 
@@ -151,8 +151,8 @@ cmake -B build-ios-device -G Xcode \
     -DCMAKE_OSX_SYSROOT=iphoneos \
     -DCMAKE_OSX_ARCHITECTURES="arm64" \
     -DCMAKE_XCODE_ATTRIBUTE_SUPPORTED_PLATFORMS=iphoneos \
-    -DCMAKE_C_FLAGS="-mcpu=apple-a12 ${COMMON_C_FLAGS}" \
-    -DCMAKE_CXX_FLAGS="-mcpu=apple-a12 ${COMMON_CXX_FLAGS}" \
+    -DCMAKE_C_FLAGS="${COMMON_C_FLAGS}" \
+    -DCMAKE_CXX_FLAGS="${COMMON_CXX_FLAGS}" \
     -S .
 cmake --build build-ios-device --config Release -- -quiet
 
@@ -161,8 +161,8 @@ cmake -B build-macos -G Xcode \
     "${COMMON_CMAKE_ARGS[@]}" \
     -DCMAKE_OSX_DEPLOYMENT_TARGET=${MACOS_MIN_OS_VERSION} \
     -DCMAKE_OSX_ARCHITECTURES="arm64;x86_64" \
-    -DCMAKE_C_FLAGS="-mcpu=apple-a12 ${COMMON_C_FLAGS}" \
-    -DCMAKE_CXX_FLAGS="-mcpu=apple-a12 ${COMMON_CXX_FLAGS}" \
+    -DCMAKE_C_FLAGS="${COMMON_C_FLAGS}" \
+    -DCMAKE_CXX_FLAGS="${COMMON_CXX_FLAGS}" \
     -S .
 cmake --build build-macos --config Release -- -quiet