use glibc strlcpy and strlcat with glibc2.38 and above

also silences warnings related to this

src/doomtype.h

@@ -130,6 +130,15 @@ char *strcasestr(const char *in, const char *what);
 #define HAVE_DOSSTR_FUNCS
 #endif
 
+#if defined (__APPLE__)
+	#define SRB2_HAVE_STRLCPY
+#elif defined (__GLIBC_PREREQ)
+	// glibc 2.38: added strlcpy and strlcat to _DEFAULT_SOURCE
+	#if __GLIBC_PREREQ(2, 38)
+		#define SRB2_HAVE_STRLCPY
+	#endif
+#endif
+
 #ifndef HAVE_DOSSTR_FUNCS
 int strupr(char *n); // from dosstr.c
 int strlwr(char *n); // from dosstr.c
@@ -137,7 +146,7 @@ int strlwr(char *n); // from dosstr.c
 
 #include <stddef.h> // for size_t
 
-#ifndef __APPLE__
+#ifndef SRB2_HAVE_STRLCPY
 #ifndef __cplusplus
 size_t strlcat(char *dst, const char *src, size_t siz);
 size_t strlcpy(char *dst, const char *src, size_t siz);

src/string.c

@@ -15,7 +15,7 @@
 #include <string.h>
 #include "doomdef.h"
 
-#if !defined (__APPLE__)
+#ifndef SRB2_HAVE_STRLCPY
 
 // Like the OpenBSD version, but it doesn't check for src not being a valid
 // C string.