riscv: add support for static PIE

In order to support static PIE the startup code must avoid relocations
before __libc_start_main is called.

sysdeps/riscv/start.S

@@ -50,7 +50,13 @@ ENTRY (ENTRY_POINT)
 	call  load_gp
 	mv    a5, a0  /* rtld_fini.  */
 	/* main may be in a shared library.  */
+#if defined PIC && !defined SHARED
+	/* Avoid relocation in static PIE since _start is called before it
+	   is relocated.  */
+	lla   a0, __wrap_main
+#else
 	la   a0, main
+#endif
 	REG_L a1, 0(sp)      /* argc.  */
 	addi  a2, sp, SZREG  /* argv.  */
 	andi  sp, sp, ALMASK /* Align stack. */
@@ -62,6 +68,11 @@ ENTRY (ENTRY_POINT)
 	ebreak
 END (ENTRY_POINT)
 
+#if defined PIC && !defined SHARED
+__wrap_main:
+	tail  main@plt
+#endif
+
 /* Dynamic links need the global pointer to be initialized prior to calling
    any shared library's initializers, so we use preinit_array to load it.
    This doesn't cut it for static links, though, since the global pointer