m-profile: Support picolibc startup mechanism

We don't need to use __cmsis_start when using picolibc; we can call main directly.

Signed-off-by: Keith Packard <keithp@keithp.com>

Author: keith-packard

CMSIS/Core/Include/m-profile/cmsis_gcc_m.h

@@ -32,6 +32,10 @@
 /* #########################  Startup and Lowlevel Init  ######################## */
 #ifndef __PROGRAM_START
 
+#ifdef __PICOLIBC__
+#include <picotls.h>
+#endif
+
 /**
   \brief   Initializes data and bss sections
   \details This default implementations initialized all data and additional bss
@@ -71,7 +75,19 @@ __STATIC_FORCEINLINE __NO_RETURN void __cmsis_start(void)
     }
   }
 
+#ifdef __PICOLIBC__
+  /* Space for errno and tcb */
+  static int __tls_area[3];
+  extern void *__tls[1];
+  __tls[0] = __tls_area;
+
+  extern int main(void);
+  (void) main();
+
+  for(;;);
+#else
   _start();
+#endif
 }
 
 #define __PROGRAM_START           __cmsis_start