glcpp: Handle '#version 0' and other invalid values

The #version directive can only handle decimal constants.  Enforce that
the value is a decimal constant.

Section 3.3 (Preprocessor) of the GLSL 4.50 spec says:

    The language version a shader is written to is specified by

        #version number profile opt

    where number must be a version of the language, following the same
    convention as __VERSION__ above.

The same section also says:

    __VERSION__ will substitute a decimal integer reflecting the version
    number of the OpenGL shading language.

Use a separate flag to track whether or not the #version line has been
encountered.  Any possible sentinel (0 is currently used) could be
specified in a #version directive.  This would lead to trying to
(internally) redefine __VERSION__.  Since there is no parser location
for this addition, NULL is passed.  This eventually results in a NULL
dereference and a segfault.

Attempts to use -1 as the sentinel would also fail if '#version
4294967295' or '#version 18446744073709551615' were used.  We should
have piglit tests for both of these.

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=97420
Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>
Cc: mesa-stable@lists.freedesktop.org
Cc: Juan A. Suarez Romero <jasuarez@igalia.com>
Cc: Karol Herbst <karolherbst@gmail.com>

src/compiler/glsl/glcpp/glcpp.h

@@ -208,6 +208,15 @@ struct glcpp_parser {
 	void *state;
 	gl_api api;
 	unsigned version;
+
+	/**
+	 * Has the #version been set?
+	 *
+	 * A separate flag is used because any possible sentinel value in
+	 * \c ::version could also be set by a #version line.
+	 */
+	bool version_set;
+
 	bool has_new_line_number;
 	int new_line_number;
 	bool has_new_source_number;