scons: Add glsl/glcpp to the include path.

Fixes this build failure on Solaris.

  Compiling build/sunos-debug/glsl/glcpp/glcpp-lex.c ...
"src/glsl/glcpp/glcpp-lex.l", line 30: cannot find include file: "glcpp-parse.h"

Signed-off-by: Vinson Lee <vlee@freedesktop.org>
Reviewed-by: Brian Paul <brianp@vmware.com>

src/glsl/SConscript

@@ -14,8 +14,8 @@ env.Prepend(CPPPATH = [
     '#src/glsl/glcpp',
 ])
 
-# Make glcpp/glcpp-parse.h and glsl_parser.h reacheable from the include path
-env.Append(CPPPATH = [Dir('.').abspath])
+# Make glcpp-parse.h and glsl_parser.h reachable from the include path.
+env.Append(CPPPATH = [Dir('.').abspath, Dir('glcpp').abspath])
 
 env.Append(YACCFLAGS = '-d')