Minimal Console: Fix compilation error

Build successfully when `platform.stdio-convert-tty-newlines` or
`platform.stdio-convert-newlines` are set to `true` by ensuring
`isatty()` is also included when `platform.stdio-minimal-console-only`
is set to `true`.

Author: hugueskamba

platform/mbed_retarget.h

@@ -573,10 +573,10 @@ extern "C" {
     ssize_t write(int fildes, const void *buf, size_t nbyte);
     ssize_t read(int fildes, void *buf, size_t nbyte);
     int fsync(int fildes);
+    int isatty(int fildes);
 #if !MBED_CONF_PLATFORM_STDIO_MINIMAL_CONSOLE_ONLY
     off_t lseek(int fildes, off_t offset, int whence);
     int ftruncate(int fildes, off_t length);
-    int isatty(int fildes);
     int fstat(int fildes, struct stat *st);
     int fcntl(int fildes, int cmd, ...);
     int poll(struct pollfd fds[], nfds_t nfds, int timeout);

platform/source/mbed_retarget.cpp

@@ -915,17 +915,13 @@ extern "C" int PREFIX(_istty)(FILEHANDLE fh)
 extern "C" int _isatty(FILEHANDLE fh)
 #endif
 {
-#if !MBED_CONF_PLATFORM_STDIO_MINIMAL_CONSOLE_ONLY
     return isatty(fh);
-#else
-    // Is attached to an interactive device
-    return 1;
-#endif // !MBED_CONF_PLATFORM_STDIO_MINIMAL_CONSOLE_ONLY
 }
 
-#if !MBED_CONF_PLATFORM_STDIO_MINIMAL_CONSOLE_ONLY
+
 extern "C" int isatty(int fildes)
 {
+#if !MBED_CONF_PLATFORM_STDIO_MINIMAL_CONSOLE_ONLY
     FileHandle *fhc = mbed_file_handle(fildes);
     if (fhc == NULL) {
         errno = EBADF;
@@ -939,8 +935,11 @@ extern "C" int isatty(int fildes)
     } else {
         return tty;
     }
-}
+#else
+    // Is attached to an interactive device
+    return 1;
 #endif // !MBED_CONF_PLATFORM_STDIO_MINIMAL_CONSOLE_ONLY
+}
 
 extern "C"
 #if defined(__ARMCC_VERSION)