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 https://github.com/libevent/libevent/commit/1f1593ff27bdf51c3e1c45b92cfb0ac931960298 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))|' \