Improve the debuginfo enablement backwards compatibility

Move the enablement logic to %__spec_install_template where it can be
buried with relatively little danger of being overridden by distros or
packagers. It's moderately annoying as the logic isn't no longer neatly in
one spot, but %__spec_install_post is commonly overridden by distros
and even packages, and in particular we don't want to have packages
copy-paste all this stuff along, because that makes making any changes
to this stuff even harder than it already is.

This should be entirely backwards compatible with all the pre-existing
%__spec_install_post overrides.

Co-authored-by: Florian Festi <[email protected]>

platform.in

@@ -57,6 +57,11 @@
 # Expanded at beginning of %install scriptlet.
 #
 
+%__spec_install_template\
+%{__spec_install_pre}\
+%[ 0%{?_enable_debug_packages} > 0 ? "%(echo "%{debug_package}" > %{specpartsdir}/rpm-debuginfo.specpart)" : "" ]\
+%{nil}
+
 %__spec_install_pre %{___build_pre}\
  %{__rm} -rf "%{buildroot}"\
  %{__mkdir_p} "%{dirname:%{buildroot}}"\
@@ -88,7 +93,6 @@
 %{nil}
 
 %__spec_install_post\
- %[ 0%{?_enable_debug_packages} > 0 ? "%(echo "%{debug_package}" > %{specpartsdir}/rpm-debuginfo.specpart)" : "" ]\
  %{?__debug_package:%{__debug_install_post}}\
  %{__arch_install_post}\
  %{__os_install_post}\