add rcrt1 start file for fully static-linked PIE

add rcrt1 start file for fully static-linked PIE

static-linked PIE files need startup code to relocate themselves, much
like the dynamic linker does. rcrt1.c reuses the code in dlstart.c,
stage 1 of the dynamic linker, which in turn reuses crt_arch.h, to
achieve static PIE with no new code. only relative relocations are
supported.

existing toolchains that don't yet support static PIE directly can be
repurposed by passing "-shared -Wl,-Bstatic -Wl,-Bsymbolic" instead of
"-static -pie" and substituting rcrt1.o in place of crt1.o.

all libraries being linked must be built as PIC/PIE; TEXTRELs are not
supported at this time.