x265: Pass --debug-prefix-map to nasm

Ensures absolute source paths are not emitted into nasm assembled objects

Fixes
WARNING: x265-3.2.1-r0 do_package_qa: QA Issue: File /usr/lib/.debug/libx265.so.179 in package x265-dbg contains reference to TMPDIR [buildpaths]

Signed-off-by: Khem Raj <raj.khem@gmail.com>

meta-multimedia/recipes-multimedia/x265/x265_3.2.1.bb

@@ -17,6 +17,10 @@ SRC_URI[sha256sum] = "fb9badcf92364fd3567f8b5aa0e5e952aeea7a39a2b864387cec31e3b5
 
 inherit lib_package pkgconfig cmake
 
+do_generate_toolchain_file:append() {
+    echo "set(CMAKE_ASM_NASM_FLAGS --debug-prefix-map ${S}=/usr/src/debug/${PN}/${EXTENDPE}${PV}-${PR})" >> ${WORKDIR}/toolchain.cmake
+}
+
 EXTRA_OECMAKE:append:x86 = " -DENABLE_ASSEMBLY=OFF"
 EXTRA_OECMAKE:append:aarch64 = " -DENABLE_PIC=ON"