- clang h743 build and run cdc_msc ok

- switch unit test back to gcc, since path to clang conflict on local setup (x86 and arm)

hw/bsp/board.c

@@ -108,6 +108,25 @@ TU_ATTR_USED int sys_read (int fhdl, char *buf, size_t count) {
 //  st->st_mode = S_IFCHR;
 //}
 
+// Clang use picolibc
+#if defined(__clang__)
+static int cl_putc(char c, FILE *f) {
+  (void) f;
+  return sys_write(0, &c, 1);
+}
+
+static int cl_getc(FILE* f) {
+  (void) f;
+  char c;
+  return sys_read(0, &c, 1) > 0 ? c : -1;
+}
+
+static FILE __stdio = FDEV_SETUP_STREAM(cl_putc, cl_getc, NULL, _FDEV_SETUP_RW);
+FILE *const stdin = &__stdio;
+__strong_reference(stdin, stdout);
+__strong_reference(stdin, stderr);
+#endif
+
 int board_getchar(void) {
   char c;
   return (sys_read(0, &c, 1) > 0) ? (int) c : (-1);