wrk: fix parallel build failure due to missing obj directory

The obj/bytecode.c rule in the wrk Makefile has no dependency on the
obj/ directory, so with parallel make luajit can run before obj/ has
been created and fails:

  LUAJIT src/wrk.lua
  luajit: .../obj/bytecode.c: No such file or directory
  make: *** [Makefile:64: obj/bytecode.c] Error 1

wrk only supports in-tree builds (relative obj/ and src/ paths, B = S),
so create ${S}/obj via do_compile[dirs], keeping ${S} last so make
still runs from the source directory.

Signed-off-by: Vaibhav Jindal <vaibjind@qti.qualcomm.com>
Signed-off-by: Khem Raj <khem.raj@oss.qualcomm.com>

meta-oe/recipes-benchmark/wrk/wrk_4.2.0.bb

@@ -23,6 +23,10 @@ EXTRA_OEMAKE = "\
     CFLAGS='${CFLAGS} -I${RECIPE_SYSROOT}/usr/include/luajit-2.1' \
 "
 
+# wrk's Makefile is in-tree only (relative obj/, src/) and its obj/bytecode.c
+# rule doesn't depend on obj/, so create it before make runs in ${S}.
+do_compile[dirs] = "${S}/obj ${S}"
+
 do_compile() {
     export LUA_PATH="${RECIPE_SYSROOT_NATIVE}/usr/share/luajit-2.1/?.lua;;"
     oe_runmake