Patch from Nicolas Pitre

In both 2.5.70-rmk1 and 2.4.19-rmk7 the syscall macros are clobering
the returned error value when building library code.

Example code:

#include <linux/unistd.h>
#include <errno.h>
extern int fake_syscall(int x, int y, int z);
_syscall3(int, fake_syscall, int, x, int, y, int, z)

Current generated code:

fake_syscall:
        @ args = 0, pretend = 0, frame = 0
        @ frame_needed = 0, uses_anonymous_args = 0
        str     lr, [sp, #-4]!
        swi     __NR_fake_syscall
        cmn     r0, #126
        ldrls   pc, [sp], #4
        bl      __errno_location
        rsb     r3, r0, #0
        str     r3, [r0, #0]
        mvn     r0, #0
        ldr     pc, [sp], #4

In the code above, whenever the return value is an error code, it
is lost due to the call to __errno_location. And because of the
asm("r0") constraint on the variable __res the compiler continues
using r0 for it even if it's now a pointer value.  errno ends up with
a totally bogus value.

With the patch below the above code becomes:

fake_syscall:
        @ args = 0, pretend = 0, frame = 0
        @ frame_needed = 0, uses_anonymous_args = 0
        stmfd   sp!, {r4, lr}
        swi     __NR_fake_syscall
        cmn     r0, #126
        mov     r4, r0
        bls     .L3
        bl      __errno_location
        rsb     r3, r4, #0
        str     r3, [r0, #0]
        mvn     r4, #0
.L3:
        mov     r0, r4
        ldmfd   sp!, {r4, pc}

which is correct.

Oh and added a small estetic change for generated code too.