libgcrypt: fix use of MACHINE_SYSROOT
libgcrypt: fix use of MACHINE_SYSROOT

Using MACHINE_SYSROOT in a recipe which has RECIPE_TYPES = "native
machine sdk" doesn't make sense, and barfs with a "cannot expand
MACHINE_SYSROOT" when trying to build one of the other types.  Use
TARGET_SYSROOT instead.

That gets us past recipe parsing, but when we then try to build
native:libgcrypt, do_configure fails since it can't find
gpg-error-config where we told it. So replace hardcoded /usr with
${target_prefix}, which expands to nothing for native and sdk and to
/usr for machine.

The configure script complains "WARNING: unrecognized options:
--without-pth" - use of pth is configured by setting --with-pth-prefix.

oe-lite/base,oe-lite/base,oe-lite/base,oe-lite/base,oe-lite/base,oe-lite/base