ci(spm): set Hafnium default LLVM path

From change Iefb14564554f7d907751ba82db6884fe7fa5c50c Hafnium requires
LLVM toolchain path to be specified in the PATH environment variable.
Set it to the toolchain stored in the project prebuilts submodule for
convenience in the CI.

Signed-off-by: Olivier Deprez <olivier.deprez@arm.com>
Change-Id: I5ad4f9f31cf151ddb227ae6d856d4095fdd03c95
diff --git a/script/build_package.sh b/script/build_package.sh
index a2461c6..75d3024 100755
--- a/script/build_package.sh
+++ b/script/build_package.sh
@@ -805,6 +805,8 @@
 
 	# Build SPM. Since build output is being directed to the build log, have
 	# descriptor 3 point to the current terminal for build wrappers to vent.
+	export PATH=$PWD/prebuilts/linux-x64/clang/bin:$PWD/prebuilts/linux-x64/dtc:$PATH
+
 	make $make_j_opts $(cat "$config_file") 3>&1 &>>"$build_log" \
 		|| fail_build
 	)