ftp/R-cran-curl: fix build on big-endian architectures

BSWAP_32 is undefined on FreeBSD, use bswap32.

It also needs sys/endian.h include.

Needed because of:

  /wrkdirs/usr/ports/ftp/R-cran-curl/work/stage/usr/local/lib/R/library/00LOCK-curl/00new/curl/libs/curl.so: Undefined symbol "BSWAP_32"

PR:		238704
Approved by:	tota (maintainer), tcberner (mentor)
Differential Revision:	https://reviews.freebsd.org/D20726

ftp/R-cran-curl/files/patch-src_curl.c

@@ -0,0 +1,20 @@
+--- src/curl.c.orig	2019-06-19 09:02:26 UTC
++++ src/curl.c
+@@ -24,6 +24,8 @@
+ #define BSWAP_32 OSSwapInt32
+ #elif (defined(__OpenBSD__))
+ #define BSWAP_32(x) swap32(x)
++#elif (defined(__FreeBSD__))
++#include <sys/endian.h>
+ #elif (defined(__GLIBC__))
+ #include <byteswap.h>
+ #define BSWAP_32(x) bswap_32(x)
+@@ -146,7 +148,7 @@ static size_t rcurl_read(void *target, size_t sz, size
+ static int rcurl_fgetc(Rconnection con) {
+   int x = 0;
+ #ifdef WORDS_BIGENDIAN
+-  return rcurl_read(&x, 1, 1, con) ? BSWAP_32(x) : R_EOF;
++  return rcurl_read(&x, 1, 1, con) ? bswap32(x) : R_EOF;
+ #else
+   return rcurl_read(&x, 1, 1, con) ? x : R_EOF;
+ #endif