Separate SYSROOT into SYSROOT_INC and SYSROOT_LINK

SYSROOT_INC for headers, and SYSROOT_LINK for libraries.
They point to the same directory, for now.

Also remove unused TARGET_CRTBEGIN*_O and TARGET_CRTEND*_O

Change-Id: Ifb60fb45cc19b2572d3497bcc1d224531a0817a1
18 files changed