Added check for glslang 15 and if that fails fallback to checking for…

… glslang 14.

CMakeLists.txt

@@ -43,8 +43,16 @@ set(VSG_MAX_INSTRUMENTATION_LEVEL 1 CACHE STRING "Set the instrumentation level
 # Enable/disable shader compilation support that pulls in glslang
 set(VSG_SUPPORTS_ShaderCompiler  1 CACHE STRING "Optional shader compiler support, 0 for off, 1 for enabled." )
 if (VSG_SUPPORTS_ShaderCompiler)
-    set(GLSLANG_MIN_VERSION "14" CACHE STRING "glslang 14 is the earliest version that we think installs itself properly on all platforms. Other platforms may be able to use an earlier version")
-    find_package(glslang ${GLSLANG_MIN_VERSION} CONFIG)
+
+    # Try looking for glslang 15 first.
+    set(GLSLANG_MIN_VERSION "15" CACHE STRING "glslang 14 is the earliest version that we think installs itself properly on all platforms. Other platforms may be able to use an earlier version")
+    find_package(glslang ${GLSLANG_MIN_VERSION} CONFIG QUIET)
+
+    if (NOT glslang_FOUND)
+        # fallback to trying glslang 14.
+        set(GLSLANG_MIN_VERSION "14")
+        find_package(glslang ${GLSLANG_MIN_VERSION} CONFIG)
+    endif()
 
     if (glslang_FOUND)
         set(FIND_DEPENDENCY_glslang "find_package(glslang ${GLSLANG_MIN_VERSION} CONFIG REQUIRED)")