add support for init/finit (constructors and destructors)

this is mainly in hopes of supporting c++ (not yet possible for other
reasons) but will also help applications/libraries which use (and more
often, abuse) the gcc __attribute__((__constructor__)) feature in "C"
code.

x86_64 and arm versions of the new startup asm are untested and may
have minor problems.

crt/i386/crt1.s

@@ -1,3 +1,5 @@
+.weak _init
+.weak _fini
 .text
 .global _start
 _start:
@@ -8,8 +10,10 @@ _start:
 	pushl %esp
 	pushl %esp
 	pushl %edx
-	pushl %ebp
-	pushl %ebp
+	call 1f
+1:	addl $[_fini-.],(%esp)
+	call 1f
+1:	addl $[_init-.],(%esp)
 	pushl %eax
 	pushl %ecx
 	call 1f

crt/i386/crti.s

@@ -0,0 +1,7 @@
+.section .init
+.global _init
+_init:
+
+.section .fini
+.global _fini
+_fini:

crt/i386/crtn.s

@@ -0,0 +1,5 @@
+.section .init
+	ret
+
+.section .fini
+	ret