Prepare to replace use of gnu-efi with the internal support

See https://github.com/systemd/systemd/pull/26641.
This will allow upstream pull request (and the main branch after the pull
request has been merged) to be built with the new code. This doesn't do
anything for official rpm builds until the new code is part of the sources.

[skip changelog]

systemd.spec

@@ -172,9 +172,6 @@ BuildRequires:  python3dist(pytest)
 BuildRequires:  python3dist(zstd)
 # gzip and lzma are provided by the stdlib
 BuildRequires:  firewalld-filesystem
-%if 0%{?have_gnu_efi}
-BuildRequires:  gnu-efi gnu-efi-devel
-%endif
 BuildRequires:  libseccomp-devel
 BuildRequires:  meson >= 0.43
 BuildRequires:  gettext
@@ -541,6 +538,16 @@ sed -r -i '/^enable systemd-boot-update.service/d' presets/90-systemd.preset
 
 sed -r 's|/system/|/user/|g' %{SOURCE16} >10-timeout-abort.conf.user
 
+%generate_buildrequires
+%if 0%{?have_gnu_efi}
+if grep -q gnu-efi meson_options.txt; then
+  echo 'gnu-efi'
+  echo 'gnu-efi-devel'
+else
+  echo 'python3dist(pyelftools)'
+fi
+%endif
+
 %build
 %global ntpvendor %(source /etc/os-release; echo ${ID})
 %{!?ntpvendor: echo 'NTP vendor zone is not set!'; exit 1}
@@ -589,7 +596,6 @@ CONFIGURE_OPTS=(
         -Dlibcurl=true
         -Dlibfido2=true
         -Defi=true
-        -Dgnu-efi=%[%{?have_gnu_efi}?"true":"false"]
         -Dtpm=true
         -Dtpm2=true
         -Dhwdb=true
@@ -647,6 +653,15 @@ CONFIGURE_OPTS=(
         # -Dsystemd-timesync-uid=, not set yet
 )
 
+if grep gnu-efi meson_options.txt; then
+  CONFIGURE_OPTS+=( -Dgnu-efi=%[%{?have_gnu_efi}?"true":"false"] )
+else
+  # For now, let's build the bootloader in the same places where we
+  # built with gnu-efi. Later on, we might want to extend coverage, but
+  # considering that that support is untested, let's not do this now.
+  CONFIGURE_OPTS+=( -Dbootloader=%[%{?have_gnu_efi}?"true":"false"] )
+fi
+
 %if %{without lto}
 %global _lto_cflags %nil
 %endif