have sh/fdpic entry point set fdpic personality if needed

the entry point code supports being loaded by a loader which is not
fdpic-aware (in practice, either kernel with mmu or qemu without fdpic
support). this mostly just works, but signal handling will wrongly use
a function descriptor address as a code address if the personality is
not adjusted to fdpic.

ideally this code could be placed with sigaction so that it's not
needed except if/when a signal handler is installed. however,
personality is incorrectly maintained per-thread by the kernel, rather
than per-process, so it's necessary to correct the personality before
any threads are started. also, in order to skip the personality
syscall when an fdpic-aware loader is used, we need to be able to
detect how the program was loaded, and this information is only
readily available at the entry point.

arch/sh/crt_arch.h

@@ -4,6 +4,18 @@ __asm__(
 ".text \n"
 ".global " START " \n"
 START ": \n"
+"	tst r8, r8 \n"
+"	bf 1f \n"
+"	mov #68, r3 \n"
+"	add r3, r3 \n"
+"	mov #8, r4 \n"
+"	swap.w r4, r4 \n"
+"	trapa #31 \n"
+"	nop \n"
+"	nop \n"
+"	nop \n"
+"	nop \n"
+"1:	nop \n"
 #ifndef SHARED
 "	mov r8, r4 \n"
 "	mova 1f, r0 \n"