alsa-tools: fix compilation error

Backport a fix from master to fix cross-compilation issues related to automake.

(From OE-Core rev: d8204a21becac6f7eb54096c6af22d6de64eb932)

Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/recipes-multimedia/alsa/alsa-tools_1.0.25.bb

@@ -20,6 +20,11 @@ SRC_URI[sha256sum] = "a974d0f3e837796f67d04df88c783aebcf4ac3c5f9ac31e2b65c10e8cb
 
 inherit autotools
 
-EXTRA_OEMAKE += "GITCOMPILE_ARGS='--host=${HOST_SYS} --build=${BUILD_SYS} --target=${TARGET_SYS} --with-libtool-sysroot=${STAGING_DIR_HOST} --prefix=${prefix}' ACLOCAL_FLAGS='-I ${STAGING_DATADIR}/aclocal'"
+EXTRA_OEMAKE += "GITCOMPILE_ARGS='--host=${HOST_SYS} --build=${BUILD_SYS} --target=${TARGET_SYS} --with-libtool-sysroot=${STAGING_DIR_HOST} --prefix=${prefix} --libdir=${libdir}' ACLOCAL_FLAGS='-I ${STAGING_DATADIR}/aclocal'"
+
+do_compile_prepend () {
+    #Automake dir is not correctly detected in cross compilation case
+    export AUTOMAKE_DIR=${STAGING_DATADIR_NATIVE}/$(ls ${STAGING_DATADIR_NATIVE} | grep automake)
+}
 
 FILES_${PN} += "${datadir}/ld10k1"