meson: remove opencl-external-clang-headers option and rely on shared-llvm

Setting opencl-external-clang-headers to enabled while using shared LLVM
was broken and this option was mostly used for windows to force static
inclusion of opencl base headers.

Simply relying on the shared-llvm option here is enough to get what we
want.

Signed-off-by: Karol Herbst <kherbst@redhat.com>
Reviewed-by: Jesse Natalie <jenatali@microsoft.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/25568>

.gitlab-ci/windows/mesa_build.ps1

@@ -59,7 +59,6 @@ meson setup `
 -Dopencl-spirv=true `
 -Dmicrosoft-clc=enabled `
 -Dstatic-libclc=all `
--Dopencl-external-clang-headers=disabled `
 -Dspirv-to-dxil=true `
 -Dbuild-tests=true `
 -Dwerror=true `

meson_options.txt

@@ -200,13 +200,6 @@ option(
   description : 'Link libclc SPIR-V statically.',
 )
 
-option(
-  'opencl-external-clang-headers',
-  type : 'feature',
-  description : 'Use system Clang headers at runtime for OpenCL kernel ' +
-                'compilation.',
-)
-
 option(
   'd3d-drivers-path',
   type : 'string',

src/compiler/clc/meson.build

@@ -30,9 +30,7 @@ _libmesaclc_c_args = []
 _libmesaclc_cpp_args = ['-DLLVM_LIB_DIR="@0@"'.format(llvm_libdir)]
 _libmesaclc_sources = []
 
-if get_option('opencl-external-clang-headers') \
-   .disable_auto_if(host_machine.system() == 'windows') \
-   .disabled()
+if not _shared_llvm
   # LLVM 16 moved clang header path from using full version to only major version
   if dep_llvm.version().version_compare('< 16')
     # Prior to LLVM 16, this path used a full version