depends: always set CMAKE_INSTALL_LIBDIR=lib/

Rather than setting this per package, set it globally, as this is always
what we want. Without doing this, later commit will have to add the same
doc + change to more packages.

depends/funcs.mk

@@ -170,12 +170,18 @@ ifneq ($($(1)_ldflags),)
 $(1)_autoconf += LDFLAGS="$$($(1)_ldflags)"
 endif
 
+# We hardcode the library install path to "lib" to match the PKG_CONFIG_PATH
+# setting in depends/config.site.in, which also hardcodes "lib".
+# Without this setting, CMake by default would use the OS library
+# directory, which might be "lib64" or something else, not "lib", on multiarch systems.
 $(1)_cmake=env CC="$$($(1)_cc)" \
                CFLAGS="$$($(1)_cppflags) $$($(1)_cflags)" \
                CXX="$$($(1)_cxx)" \
                CXXFLAGS="$$($(1)_cppflags) $$($(1)_cxxflags)" \
                LDFLAGS="$$($(1)_ldflags)" \
-             cmake -DCMAKE_INSTALL_PREFIX:PATH="$$($($(1)_type)_prefix)" $$($(1)_config_opts)
+               cmake -DCMAKE_INSTALL_PREFIX:PATH="$$($($(1)_type)_prefix)" \
+               -DCMAKE_INSTALL_LIBDIR=lib/ \
+               $$($(1)_config_opts)
 ifeq ($($(1)_type),build)
 $(1)_cmake += -DCMAKE_INSTALL_RPATH:PATH="$$($($(1)_type)_prefix)/lib"
 else