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.

gdb/testsuite/ChangeLog

@@ -1,3 +1,7 @@
+2016-02-15  Jan Kratochvil  <jan.kratochvil@redhat.com>
+
+	* gdb.arch/i386-prologue.c: Add missing prototypes.
+
 2016-02-15  Jan Kratochvil  <jan.kratochvil@redhat.com>
 
 	* gdb.arch/i386-gnu-cfi.exp: Use standard_output_file.

gdb/testsuite/gdb.arch/i386-prologue.c

@@ -27,6 +27,10 @@ void gdb1253 (void);
 void gdb1718 (void);
 void gdb1338 (void);
 void jump_at_beginning (void);
+void standard (void);
+void stack_align_ecx (void);
+void stack_align_edx (void);
+void stack_align_eax (void);
 
 int
 main (void)