package_rpm: set a timestamp handling policy with the new macro %build_mtime_policy

There is the following warning when the do_package_write_rpm task is executed
when bitbake linux-yocto:
  warning: %clamp_mtime_to_source_date_epoch is deprecated, please use %build_mtime_policy

After RPM is upgraded to 4.20.0, the %clamp_mtime_to_source_date_epoch macro is
now deprecated in favor of %build_mtime_policy set to clamp_to_source_date_epoch.

(From OE-Core rev: fa9b9e599bbf3ac73c7a9b1d15ccb0e0bbbe4c11)

Signed-off-by: Bin Lan <bin.lan.cn@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/classes-global/package_rpm.bbclass

@@ -699,7 +699,7 @@ python do_package_rpm () {
     cmd = cmd + " --define '_smp_ncpus_max 4'"
     cmd = cmd + " --define '_source_payload %s'" % rpmbuild_compmode
     cmd = cmd + " --define '_binary_payload %s'" % rpmbuild_compmode
-    cmd = cmd + " --define 'clamp_mtime_to_source_date_epoch 1'"
+    cmd = cmd + " --define 'build_mtime_policy clamp_to_source_date_epoch'"
     cmd = cmd + " --define 'use_source_date_epoch_as_buildtime 1'"
     cmd = cmd + " --define '_buildhost reproducible'"
     cmd = cmd + " --define '__font_provides %{nil}'"