rpm: write macros under libdir

If we create a macros file under etc/, the populate_sdk task would
fail if 'package-management' is in SDKIMAGE_FEATURES and nativesdk-rpm-build
is installed.. The error message is like below:

  unable to place /.../sdk/image/etc/rpm in final SDK location

This is because it's trying to move the etc/rpm dictory into the
host sysroot but the <host_sysroot>/etc/rpm has already exists.

To solve this problem, avoid creating /etc/rpm/macros for nativesdk-rpm-build,
use ${libdir}/macros instead. In this way, the macros file is hold
in nativesdk-rpm. As nativesdk-rpm-build depends on nativesdk-rpm,
the 'rpmbuild' command inside SDK can still correctly find find-debuginfo
binary.

(From OE-Core rev: 2a13a671910cad68ab962ce369b9ed60a9bf7eea)

Signed-off-by: Chen Qi <Qi.Chen@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
(cherry picked from commit 5fde0eadf16d34d88a599009013913fe55d89283)
Signed-off-by: Steve Sakoman <steve@sakoman.com>

meta/recipes-devtools/rpm/rpm_4.18.1.bb

@@ -134,8 +134,8 @@ do_install:append:class-target() {
 do_install:append:class-nativesdk() {
     rm -rf ${D}${SDKPATHNATIVE}/var
     # Ensure find-debuginfo is located correctly inside SDK
-    mkdir -p ${D}${SDKPATHNATIVE}/etc/rpm
-    echo "%__find_debuginfo   ${SDKPATHNATIVE}/usr/bin/find-debuginfo" >> ${D}${SDKPATHNATIVE}/etc/rpm/macros
+    mkdir -p ${D}${libdir}/rpm
+    echo "%__find_debuginfo   ${SDKPATHNATIVE}/usr/bin/find-debuginfo" >> ${D}${libdir}/rpm/macros
 }
 
 do_install:append () {
@@ -173,7 +173,6 @@ FILES:${PN}-build = "\
     ${libdir}/rpm/macros.p* \
     ${libdir}/rpm/fileattrs/* \
 "
-FILES:${PN}-build:append:class-nativesdk = " ${SDKPATHNATIVE}/etc/rpm/macros"
 
 FILES:${PN}-sign = "\
     ${bindir}/rpmsign \