[client] egl: use new util_hasGLExt helper to check extensions

We previously used strstr, which can be prone to false positives when
the name of one extension is a substring of another extension.

This commit creates the helper function util_hasGLExt, which asserts
that the substring found in extension list is bounded by either spaces
or the beginning/end of the string.

common/include/common/stringutils.h

@@ -20,6 +20,8 @@ Place, Suite 330, Boston, MA 02111-1307 USA
 #ifndef _H_LG_COMMON_STRINGUTILS
 #define _H_LG_COMMON_STRINGUTILS
 
+#include <stdbool.h>
+
 // vsprintf but with buffer allocation
 int valloc_sprintf(char ** str, const char * format, va_list ap)
   __attribute__ ((format (printf, 2, 0)));
@@ -28,4 +30,7 @@ int valloc_sprintf(char ** str, const char * format, va_list ap)
 int alloc_sprintf(char ** str, const char * format, ...)
   __attribute__ ((format (printf, 2, 3)));
 
+// Find value in a list separated by delimiter.
+bool str_containsValue(const char * list, char delimiter, const char * value);
+
 #endif

common/src/stringutils.c

@@ -17,9 +17,13 @@ this program; if not, write to the Free Software Foundation, Inc., 59 Temple
 Place, Suite 330, Boston, MA 02111-1307 USA
 */
 
+#include <stdbool.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <stdarg.h>
+#include <string.h>
+
+#include "common/stringutils.h"
 
 int valloc_sprintf(char ** str, const char * format, va_list ap)
 {
@@ -64,3 +68,23 @@ int alloc_sprintf(char ** str, const char * format, ...)
   va_end(ap);
   return ret;
 }
+
+bool str_containsValue(const char * list, char delimiter, const char * value)
+{
+  size_t len = strlen(value);
+  const char span[] = {delimiter, '\0'};
+
+  while (*list)
+  {
+    if (*list == delimiter)
+    {
+      ++list;
+      continue;
+    }
+    size_t n = strcspn(list, span);
+    if (n == len && strncmp(value, list, n) == 0)
+      return true;
+    list += n;
+  }
+  return false;
+}