Merge bitcoin/bitcoin#31358: depends: Avoid hardcoding host_prefix in toolchain file

d9c8aacce3 depends, refactor: Avoid hardcoding `host_prefix` in toolchain file (Hennadii Stepanov)

Pull request description:

  This PR allows the entire `depends/<host_prefix>` directory to be relocatable.

  Only `libevent` package configuration files are non-relocatable for the version `2.1.12-stable` we use now. However, this issue has been fixed upstream in 1f1593ff27 and friends.

  Fixes https://github.com/bitcoin/bitcoin/issues/31050.

ACKs for top commit:
  theuni:
    Neat. utACK d9c8aacce3
  ryanofsky:
    Code review ACK d9c8aacce3

Tree-SHA512: c4c340722e63fc1da36fba2b15f025a6e1d477da1991194d678f546f2f3ea9454e2f0ff054aae6ae6c332a0781a597c3ce63b9018b46b8c258033f0d19efbef3

depends/Makefile

@@ -217,7 +217,6 @@ $(host_prefix)/toolchain.cmake : toolchain.cmake.in $(host_prefix)/.stamp_$(fina
             -e 's|@STRIP@|$(host_STRIP)|' \
             -e 's|@OBJCOPY@|$(host_OBJCOPY)|' \
             -e 's|@OBJDUMP@|$(host_OBJDUMP)|' \
-            -e 's|@depends_prefix@|$(host_prefix)|' \
             -e 's|@CFLAGS@|$(strip $(host_CFLAGS))|' \
             -e 's|@CFLAGS_RELEASE@|$(strip $(host_release_CFLAGS))|' \
             -e 's|@CFLAGS_DEBUG@|$(strip $(host_debug_CFLAGS))|' \

depends/toolchain.cmake.in

@@ -81,12 +81,12 @@ set(CMAKE_OBJDUMP "@OBJDUMP@")
 # affected by a potentially random environment.
 set(CMAKE_FIND_USE_CMAKE_ENVIRONMENT_PATH OFF)
 
-set(CMAKE_FIND_ROOT_PATH "@depends_prefix@")
+set(CMAKE_FIND_ROOT_PATH "${CMAKE_CURRENT_LIST_DIR}")
 set(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER)
 set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)
 set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)
 set(CMAKE_FIND_ROOT_PATH_MODE_PACKAGE ONLY)
-set(QT_TRANSLATIONS_DIR "@depends_prefix@/translations")
+set(QT_TRANSLATIONS_DIR "${CMAKE_CURRENT_LIST_DIR}/translations")
 
 if(CMAKE_SYSTEM_NAME STREQUAL "Darwin" AND NOT CMAKE_HOST_APPLE)
   # The find_package(Qt ...) function internally uses find_library()