Merge bitcoin/bitcoin#25046: build: Fix libmultiprocess cross-compiling to Linux hosts

c0f5cc1 build: Fix `libmultiprocess` cross-compiling to Linux hosts (Hennadii Stepanov)

Pull request description:

  To successfully call the [`capnp_generate_cpp()`](https://github.com/chaincodelabs/libmultiprocess/blob/d576d975debdc9090bd2582f83f49c76c0061698/CMakeLists.txt#L45) function, the `libmultiprocess` build system must be provided with paths to the native `capnp` and `capnpc-c++` tools.

  This [comment](bitcoin/bitcoin#24387 (comment)) points the same:
  > I think `packages/libmultiprocess.mk` probably needs to be passing a `-DCAPNP_EXECUTABLE=.../depends/arm-linux-gnueabihf/native/bin/capnp` argument to cmake. Also the package should have dependencies on both `capnp` and `native_capnp`.

  Fixes bitcoin/bitcoin#24387.

ACKs for top commit:
  ryanofsky:
    Code review ACK c0f5cc1

Tree-SHA512: 2986d8bf98d2761eceba21b1897145c5185a0922d4c2084e8812d4d07dc94237e5c2809036641c4f7c491a3414727fff328cba91ce138b89e37ec5cba61d8f61

Author: fanquake

depends/funcs.mk

@@ -175,7 +175,7 @@ $(1)_cmake=env CC="$$($(1)_cc)" \
                CXX="$$($(1)_cxx)" \
                CXXFLAGS="$$($(1)_cppflags) $$($(1)_cxxflags)" \
                LDFLAGS="$$($(1)_ldflags)" \
-             cmake -DCMAKE_INSTALL_PREFIX:PATH="$$($($(1)_type)_prefix)"
+             cmake -DCMAKE_INSTALL_PREFIX:PATH="$$($($(1)_type)_prefix)" $$($(1)_cmake_opts)
 ifeq ($($(1)_type),build)
 $(1)_cmake += -DCMAKE_INSTALL_RPATH:PATH="$$($($(1)_type)_prefix)/lib"
 else

depends/packages/libmultiprocess.mk

@@ -4,6 +4,16 @@ $(package)_download_path=$(native_$(package)_download_path)
 $(package)_file_name=$(native_$(package)_file_name)
 $(package)_sha256_hash=$(native_$(package)_sha256_hash)
 $(package)_dependencies=native_$(package) capnp
+ifneq ($(host),$(build))
+$(package)_dependencies += native_capnp
+endif
+
+define $(package)_set_vars :=
+ifneq ($(host),$(build))
+$(package)_cmake_opts := -DCAPNP_EXECUTABLE="$$(native_capnp_prefixbin)/capnp"
+$(package)_cmake_opts += -DCAPNPC_CXX_EXECUTABLE="$$(native_capnp_prefixbin)/capnpc-c++"
+endif
+endef
 
 define $(package)_config_cmds
   $($(package)_cmake) .