depends: always install libmultiprocess to /lib

On some systems, libmultiprocess would be installed into `lib64`, I
assume due to the use of GNUInstallDirs, however all other libs we build
in depends, go into lib/. Rather than adding lib64/ to the pkg-config
and link flags, I opted for always installing into lib/.

This was changed in
bitcoin-core/libmultiprocess#79 upstream.

Co-authored-by: Ryan Ofsky <ryan@ofsky.org>

Author: fanquake

depends/packages/libmultiprocess.mk

@@ -8,7 +8,12 @@ ifneq ($(host),$(build))
 $(package)_dependencies += native_capnp
 endif
 
+# Hardcode 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.
 define $(package)_set_vars :=
+$(package)_config_opts += -DCMAKE_INSTALL_LIBDIR=lib/
 ifneq ($(host),$(build))
 $(package)_config_opts := -DCAPNP_EXECUTABLE="$$(native_capnp_prefixbin)/capnp"
 $(package)_config_opts += -DCAPNPC_CXX_EXECUTABLE="$$(native_capnp_prefixbin)/capnpc-c++"