clang needs stdlib included in a couple of files

[sptrakesh]

Hello,

Compilation fails on Apple Clang as a couple of files need to include stdlib.h.

Please add includes to turbob64c.c and turbob64v128.c.

diff --git a/turbob64c.c b/turbob64c.c
index f52be2d..8598f1d 100644
--- a/turbob64c.c
+++ b/turbob64c.c
@@ -24,6 +24,7 @@
 // Turbo-Base64: Scalar encode
 #include "turbob64_.h"
 #include "turbob64.h"
+#include <stdlib.h>
 
 size_t tb64enclen(size_t n) { return TB64ENCLEN(n); }
  
diff --git a/turbob64v128.c b/turbob64v128.c
index b1f2ba0..d0cdc4d 100644
--- a/turbob64v128.c
+++ b/turbob64v128.c
@@ -24,6 +24,7 @@
 //  Turbo-Base64: ssse3 + arm neon functions (see also turbob64v256)
 
 #include <string.h>
+#include <stdlib.h>
 
   #if defined(__AVX__)
 #include <immintrin.h>