Add missing gdb.arch/i386-prologue.c prototypes

Add missing gdb.arch/i386-prologue.c prototypes

The testfile has not ran because:
gdb.arch/i386-prologue.c:34:3: warning: implicit declaration of function 'standard' [-Wimplicit-function-declaration]
   standard ();
   ^
gdb.arch/i386-prologue.c:35:3: warning: implicit declaration of function 'stack_align_ecx' [-Wimplicit-function-declaration]
   stack_align_ecx ();
   ^
gdb.arch/i386-prologue.c:36:3: warning: implicit declaration of function 'stack_align_edx' [-Wimplicit-function-declaration]
   stack_align_edx ();
   ^
gdb.arch/i386-prologue.c:37:3: warning: implicit declaration of function 'stack_align_eax' [-Wimplicit-function-declaration]
   stack_align_eax ();
   ^

gdb/testsuite/ChangeLog
2016-02-15  Jan Kratochvil  <jan.kratochvil@redhat.com>

	* gdb.arch/i386-prologue.c: Add missing prototypes.