qemuppc: Simplify bsp_specs

Updates #3520.

c/src/lib/libbsp/powerpc/qemuppc/bsp_specs

@@ -4,8 +4,7 @@
 
 *startfile:
 %{!qrtems: %(old_startfile)} \
-%{!nostdlib: %{qrtems: ecrti%O%s rtems_crti%O%s crtbegin.o%s \
-    start.o%s -e _start -u __vectors}}
+%{!nostdlib: %{qrtems: ecrti%O%s rtems_crti%O%s crtbegin.o%s}}
 
 *endfile:
 %{!qrtems: %(old_endfile)} %{qrtems: crtend.o%s ecrtn.o%s}

c/src/lib/libbsp/powerpc/qemuppc/startup/linkcmds

@@ -2,6 +2,9 @@ OUTPUT_FORMAT("elf32-powerpc", "elf32-powerpc",
               "elf32-powerpc")
 OUTPUT_ARCH(powerpc:common)
 ENTRY(_start)
+STARTUP(start.o)
+EXTERN(__vectors)
+
 MEMORY
   {
         RAM       : ORIGIN = 0, LENGTH = 4M