analyze: introduce cpu-features command

This may be useful when configuring the ConditionCPUFeature= setting.

man/systemd-analyze.xml

@@ -224,6 +224,12 @@
       <arg choice="plain">architectures</arg>
       <arg choice="opt" rep="repeat"><replaceable>NAME</replaceable></arg>
     </cmdsynopsis>
+    <cmdsynopsis>
+      <command>systemd-analyze</command>
+      <arg choice="opt" rep="repeat">OPTIONS</arg>
+      <arg choice="plain">cpu-features</arg>
+      <arg choice="opt" rep="repeat"><replaceable>NAME</replaceable></arg>
+    </cmdsynopsis>
     <cmdsynopsis>
       <command>systemd-analyze</command>
       <arg choice="opt" rep="repeat">OPTIONS</arg>
@@ -1159,6 +1165,30 @@ x86-64      native</programlisting>
       </example>
     </refsect2>
 
+    <refsect2>
+      <title><command>systemd-analyze cpu-features <optional><replaceable>NAME</replaceable>...</optional></command></title>
+
+      <para>Lists all known CPU features for the system's CPU architecture, indicating which of them are
+      supported. The listed feature names are those understood by <varname>ConditionCPUFeature=</varname>;
+      see <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+      for details. If one or more feature names are specified, only those are listed.</para>
+
+      <para>The command is currently supported only on arm64, x86, and x86_64 systems.</para>
+
+      <example>
+        <title>Table output on an x86_64 system</title>
+        <programlisting>$ systemd-analyze cpu-features
+NAME         SUPPORT
+abm          ✓
+adx          ✓
+aes          ✓
+apic         ✓
+avx          ✓
+avx2         ✓
+…</programlisting>
+      </example>
+    </refsect2>
+
     <refsect2>
       <title><command>systemd-analyze smbios11</command></title>
 

man/systemd.unit.xml

@@ -2058,6 +2058,11 @@
           among others. For the full list, see the documentation on
           <ulink url="https://docs.kernel.org/arch/arm64/elf_hwcaps.html">ARM64 ELF hwcaps</ulink>.</para>
 
+          <para>See
+          <citerefentry><refentrytitle>systemd-analyze</refentrytitle><manvolnum>1</manvolnum></citerefentry>'s
+          <command>cpu-features</command> command for the complete list of known CPU features for the system.
+          </para>
+
           <para>To avoid ambiguities in mixed-architecture fleets, the value can be prefixed
           with the architecture name using the form <literal>ARCH.FEATURE</literal>. If the
           architecture prefix does not match the running system, the condition evaluates