Fix platform macros.. (#9502)

Both `SLANG_WASM` and `SLANG_PROCESSOR_WASM` now default to `0` if not
available, same as with all other platform definitions.

Author: skallweitNV

include/slang.h

@@ -162,6 +162,9 @@ Most applications should not need to touch this section.
     #ifndef SLANG_WIIU
         #define SLANG_WIIU 0
     #endif
+    #ifndef SLANG_WASM
+        #define SLANG_WASM 0
+    #endif
 #endif /* SLANG_PLATFORM */
 
 /* Shorthands for "families" of compilers/platforms */
@@ -450,6 +453,10 @@ convention for interface methods.
     #define SLANG_PROCESSOR_POWER_PC_64 0
 #endif
 
+#ifndef SLANG_PROCESSOR_WASM
+    #define SLANG_PROCESSOR_WASM 0
+#endif
+
 // Processor families
 
 #define SLANG_PROCESSOR_FAMILY_X86 (SLANG_PROCESSOR_X86_64 | SLANG_PROCESSOR_X86)