CMake: Only require SPIRV-Cross when enabling OpenGL backend

Change-Id: Ie6be1301c3f2f9877a9dfb04ab5025559b90d926
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/64741
Reviewed-by: Austin Eng <enga@chromium.org>
Reviewed-by: Stephen White <senorblanco@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Ben Clayton <bclayton@google.com>

CMakeLists.txt

@@ -107,6 +107,12 @@ if (${DAWN_ENABLE_DESKTOP_GL} OR ${DAWN_ENABLE_OPENGLES})
     set(DAWN_ENABLE_OPENGL ON)
 endif()
 
+# OpenGL backend requires SPIRV-Cross
+set(DAWN_REQUIRES_SPIRV_CROSS OFF)
+if (DAWN_ENABLE_OPENGL)
+    set(DAWN_REQUIRES_SPIRV_CROSS ON)
+endif()
+
 ################################################################################
 # Dawn's public and internal "configs"
 ################################################################################

src/dawn_native/CMakeLists.txt

@@ -185,13 +185,16 @@ target_link_libraries(dawn_native
             dawn_platform
             dawn_internal_config
             libtint
-            spirv-cross-core
-            spirv-cross-glsl
-            spirv-cross-hlsl
-            spirv-cross-msl
             SPIRV-Tools-opt
 )
 
+if (DAWN_REQUIRES_SPIRV_CROSS)
+    target_link_libraries(dawn_native PRIVATE spirv-cross-core)
+    if (DAWN_ENABLE_OPENGL)
+        target_link_libraries(dawn_native PRIVATE spirv-cross-glsl)
+    endif()
+endif()
+
 if (DAWN_USE_X11)
     find_package(X11 REQUIRED)
     target_link_libraries(dawn_native PRIVATE ${X11_LIBRARIES})

third_party/CMakeLists.txt

@@ -12,7 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-if (NOT TARGET spirv-cross)
+if (DAWN_REQUIRES_SPIRV_CROSS AND NOT TARGET spirv-cross)
     set(SPIRV_CROSS_EXCEPTIONS_TO_ASSERTIONS ON CACHE BOOL "" FORCE)
     set(SPIRV_CROSS_ENABLE_TESTS OFF CACHE BOOL "" FORCE)
     set(SPIRV_CROSS_SKIP_INSTALL ON CACHE BOOL "" FORCE)