Implement S_realloc

(cherry picked from commit 5efb59c)

Author: steve-s

CHANGELOG.md

@@ -5,6 +5,10 @@ New features:
 * the default `Renviron` file sets `R_LIBS_USER` to a directory inside the current user's home
   * running the `configure_fastr` will change this to a path that also contains GraalVM version and will create the directory
 
+Added missing C APIs:
+
+* `S_realloc`
+
 Bug fixes:
 
 * fatal error on Linux when pressing CTRL+C during long computation
@@ -23,7 +27,7 @@ Bug fixes:
 * new Truffle interop converts `double` values to `int` values if they fit in the integer range
   * see the changes in the [spec tests](https://github.com/oracle/fastr/commit/e08e2b19571479dddb6167d9a1d492a14cb4c7b2#diff-c842fa11097793b19bd410589c36af99)
 
-Added missing R builtins and C APIa
+Added missing R builtins and C APIs
 
 * simple support for the weak reference API functions (`R_MakeWeakRef`, `R_MakeWeakRefC`, `R_WeakRefKey`, `R_WeakRefValue`)
 * `Rf_i1mach`

com.oracle.truffle.r.native/fficall/src/truffle_nfi/Memory.c

@@ -1,7 +1,7 @@
 /*
  * Copyright (c) 1995-2015, The R Core Team
  * Copyright (c) 2003, The R Foundation
- * Copyright (c) 2015, 2018, Oracle and/or its affiliates
+ * Copyright (c) 2015, 2019, Oracle and/or its affiliates
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -37,8 +37,11 @@ char *S_alloc(long n, int size) {
     return p;
 }
 
-char *S_realloc(char *p, long a, long b, int size) {
-    return unimplemented("S_realloc");
+char *S_realloc(char *p, long new_size, long old_size, int elt_size) {
+    char* res = R_alloc(new_size, elt_size);
+    long min_size = new_size < old_size ? new_size : old_size;
+    memcpy(res, p, min_size * elt_size);
+    return res;
 }
 
 void *R_chk_calloc(size_t nelem, size_t elsize) {