Provides stack-cleaning compilers for x86_64:

 * as
 * cc
 * c++
 * fortran

Each of them modify the generated/given X86_64 assembly by prepending stack-cleanup code to each function:

	movq $0x7ffff7ff8000, %r11
	cmpq %r11, %rsp
	jbe .Lstack_cleaner_done0
	movq $QSIZE, %r11
.Lstack_cleaner_loop0:
        movq $0, OFFSET(%rsp,%r11,8)
        subq $1, %r11
        jne  .Lstack_cleaner_loop0:
.Lstack_cleaner_done0:

The modification of the assembly is done by the clean-stack-filter program.

If the underlying compiler is clang, it might be necessary to add the -no-integrated-as flag in order to force the
usage of an external assembler.
