Hexagon architecture build fixes + builtins

Small build fixes applied:
- use -mlong-calls to build
- extend jumps in futex_atomic_*
- etc

Also, for convenience and portability, the hexagon compiler builtin
functions like memcpy etc have been added to the kernel -- following the
idiom used by other architectures.
Hexagon: add target builtins to kernel

Add the compiler-rt builtins like memcpy to the hexagon kernel.

Signed-off-by: Sid Manning <sidneym@codeaurora.org>
Add SYM_FUNC_START/END, ksyms exports
Signed-off-by: Brian Cain <bcain@codeaurora.org>

Tested-by: Nick Desaulniers <ndesaulniers@google.com>
8 files changed