Look for crates in LIBDIR, provided by --libdir option

Fixies #11671

This commit changes default relative libdir 'lib' to a relative libdir calculated using LIBDIR provided by --libdir configuration option. In case if no option was provided behavior does not change.

This can be simplified by using:
```
ifeq ($$(CFG_WINDOWSY_$(3))-$(1),0-0)
HLIB$(1)_H_$(3) = $$(HROOT$(1)_H_$(3))/lib
else
HLIB$(1)_H_$(3) = $$(HROOT$(1)_H_$(3))/$$(CFG_LIBDIR_RELATIVE)
endif
```