PP: don't give errors on some tokens under #if 0 (or similar).

Fixes #1295.

Tokens that are accepted by any version of HLSL or GLSL should be
allowed when #ifdef'd off, such that errors are not reported.

Test/baseResults/cppRelaxSkipTokensErrors.vert.out

@@ -0,0 +1,14 @@
+cppRelaxSkipTokensErrors.vert
+Shader version: 110
+0:? Sequence
+0:?   Linker Objects
+
+
+Linked vertex stage:
+
+ERROR: Linking vertex stage: Missing entry point: Each stage requires one entry point
+
+Shader version: 110
+0:? Sequence
+0:?   Linker Objects
+

Test/cppBad.vert

@@ -1,5 +1,5 @@
 #define m#0#
 #if m
-
+#endif
 #define n()
 int n"

Test/cppRelaxSkipTokensErrors.vert

@@ -0,0 +1,14 @@
+#version 110
+
+#if 0
+3.5L
+3.5h
+2034h
+1.#INF
+0x1234567812345L
+12323394203923879234L
+0123s;
+123s;
+0123456712345671234L
+"string"
+#endif