Changes

Update link options for PowerPC 32 bits Linux (#9572)

On PowerPC 32 bits Linux, recent versions of GCC produce "secure PLT"
relocatable code by default, while ocamlopt still generates "BSS PLT"
relocatable code.  This causes a warning at link-time when "BSS PLT"
object files (produced by ocamlopt) are being linked.

This PR makes sure that "-mbss-plt" is added to the OC_LDFLAGS and
MKSHAREDLIB variables on PowerPC 32 bits Linux.
 (commit: a364988)