Look for some symbols using check_symbol_exists to help newer Visual Studio.

Reported by Gerard ODonnell in #231.
diff --git a/CMakeLists.txt b/CMakeLists.txt
index afcc6fc..dca3617 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -92,9 +92,9 @@
 check_function_exists(_fdopen HAVE__FDOPEN)
 check_function_exists(_fileno HAVE__FILENO)
 check_function_exists(_setmode HAVE__SETMODE)
-check_function_exists(_snprintf HAVE__SNPRINTF)
+check_symbol_exists(_snprintf stdio.h HAVE__SNPRINTF)
 check_function_exists(_strdup HAVE__STRDUP)
-check_function_exists(_stricmp HAVE__STRICMP)
+check_symbol_exists(_stricmp string.h HAVE__STRICMP)
 check_function_exists(_strtoi64 HAVE__STRTOI64)
 check_function_exists(_strtoui64 HAVE__STRTOUI64)
 check_function_exists(_unlink HAVE__UNLINK)
@@ -108,7 +108,7 @@
 check_function_exists(getprogname HAVE_GETPROGNAME)
 check_function_exists(localtime_r HAVE_LOCALTIME_R)
 check_function_exists(setmode HAVE_SETMODE)
-check_function_exists(strcasecmp HAVE_STRCASECMP)
+check_symbol_exists(strcasecmp strings.h HAVE_STRCASECMP)
 check_function_exists(strdup HAVE_STRDUP)
 check_function_exists(stricmp HAVE_STRICMP)
 check_function_exists(strtoll HAVE_STRTOLL)
diff --git a/THANKS b/THANKS
index b7e4497..8482c29 100644
--- a/THANKS
+++ b/THANKS
@@ -43,6 +43,7 @@
 François Simon <AT.GFI.Francois.SIMON@sesam-vitale.fr>
 Frederik Ramm <frederik@remote.org>
 gk7huki <gk7huki@gmail.com>
+Gerard ODonnell
 Hanno Böck <hanno@hboeck.de>
 HeeMyung
 Heiko Becker