distutils.bbclass: override LDSHARED so we use the linker for this build and not the one used in sstate-cache

Without this fix, when packages are being built using distutils and
the python packages were deployed from sstate-cache is it possible
that the LD command will contain an invalid sysroot override.

We can fix this by always exported LDSHARED, which is the env var
that distutil looks for to override creating shared libraries.

(From OE-Core rev: 3f6b859a29ba7f570b9dae3b5bb7ab4bd7b8cee4)

Signed-off-by: Matthew McClintock <msm@freescale.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/classes/distutils.bbclass

@@ -72,3 +72,5 @@ distutils_do_install() {
 }
 
 EXPORT_FUNCTIONS do_compile do_install
+
+export LDSHARED="${CCLD} -shared"