Merge #20046: depends: Set CMAKE_INSTALL_RPATH for native packages

7d0271b depends: Set CMAKE_INSTALL_RPATH for native packages (Russell Yanofsky)

Pull request description:

  This PR is part of the [process separation project](https://github.com/bitcoin/bitcoin/projects/10).

  ---

  After #19685 started setting `LDFLAGS`, the `INSTALL_RPATH_USE_LINK_PATH` cmake option used in the libmultiprocess build no longer works, so it is neccessary to set `CMAKE_INSTALL_RPATH` as a fallback.

  It's unclear currently whether the bad interaction between `INSTALL_RPATH_USE_LINK_PATH` and `LDFLAGS` is a bug, but the issue is reported:

  - bitcoin/bitcoin#19981 (comment)
  - https://discourse.cmake.org/t/install-rpath-use-link-path-not-working-when-cmake-exe-linker-flags-ldflags-is-set/1892

  Fixes #19981

ACKs for top commit:
  fanquake:
    ACK 7d0271b - I haven't looked in depth, but I've re-read through #19981 and checked the failure by testing #19160 (with this reverted):
  dongcarl:
    ACK 7d0271b Looked into this a bit, it makes sense that for the things we build in depends, we want the library search to start in depends. It seems reasonable to expect this to happen automatically when `CMAKE_INSTALL_PREFIX` and `INSTALL_RPATH_USE_LINK_PATH` are set, but oh well...

Tree-SHA512: 97cc5801c3204c14cd33004423631456ca0701e2127ee5146810a76e2f4aac9de1f4b5437402a4329cda54e022dc99270fee7e38c2995765f36b3848215fa78e

Author: fanquake

depends/funcs.mk

@@ -163,7 +163,9 @@ $(1)_cmake=env CC="$$($(1)_cc)" \
                CXXFLAGS="$$($(1)_cppflags) $$($(1)_cxxflags)" \
                LDFLAGS="$$($(1)_ldflags)" \
              cmake -DCMAKE_INSTALL_PREFIX:PATH="$$($($(1)_type)_prefix)"
-ifneq ($($(1)_type),build)
+ifeq ($($(1)_type),build)
+$(1)_cmake += -DCMAKE_INSTALL_RPATH:PATH="$$($($(1)_type)_prefix)/lib"
+else
 ifneq ($(host),$(build))
 $(1)_cmake += -DCMAKE_SYSTEM_NAME=$($(host_os)_cmake_system)
 $(1)_cmake += -DCMAKE_C_COMPILER_TARGET=$(host)