The firmware is cross-compiled, but the build system ends up using
'objcopy' instead of 'xtensa-elf-objcopy' by default.  Force it to
use the right one.

--- source/target_firmware/configure	2014-10-28 20:57:26.834436561 +0100
+++ source/target_firmware/configure	2014-10-28 20:57:29.666436530 +0100
@@ -11,6 +11,7 @@ mkdir -p build
 cat > "$TOOLCHAIN_FILE" <<EOF
 INCLUDE(CMakeForceCompiler)
 
+SET(CMAKE_OBJCOPY xtensa-elf-objcopy)
 SET(CMAKE_SYSTEM_PROCESSOR xtensa)
 SET(CMAKE_FIND_ROOT_PATH ${TOOLCHAIN}/$TARGET)
 SET(CMAKE_STRIP :)
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<tr><td><span title='2019-02-05 12:03:25 +0100'>2019-02-05</span></td><td><a href='/guix/commit/tests/status.scm?id=ba514b601ba6be15b823e0a12d4b6e42f9d2489e'>status: Keep track of the current build phase.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
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