unix: Show compiler info in REPL banner.

The unix port's main.c gets used by unix and windows ports, and with a
variety of compilers, so it's convenient to see which version is actually
being used immediately when starting micropython.  This is similar to what
CPython does.

ports/unix/main.c

@@ -47,6 +47,7 @@
 #include "py/mphal.h"
 #include "py/mpthread.h"
 #include "extmod/misc.h"
+#include "extmod/moduplatform.h"
 #include "extmod/vfs.h"
 #include "extmod/vfs_posix.h"
 #include "genhdr/mpversion.h"
@@ -178,7 +179,8 @@ STATIC char *strjoin(const char *s1, int sep_char, const char *s2) {
 
 STATIC int do_repl(void) {
     mp_hal_stdout_tx_str("MicroPython " MICROPY_GIT_TAG " on " MICROPY_BUILD_DATE "; "
-        MICROPY_PY_SYS_PLATFORM " version\nUse Ctrl-D to exit, Ctrl-E for paste mode\n");
+        MICROPY_PY_SYS_PLATFORM " [" MICROPY_PLATFORM_COMPILER "] version\n"
+        "Use Ctrl-D to exit, Ctrl-E for paste mode\n");
 
     #if MICROPY_USE_READLINE == 1