Unfortunately XSLT 1.0 only supports the property xsl:vendor so you will need to check
<xsl:text>XSLT Processor: </xsl:text>
<xsl:value-of select="system-property('xsl:vendor')" />
<xsl:if test="system-property('xsl:version') = '2.0'">
<xsl:value-of select="system-property('xsl:product-name')"/>
<xsl:value-of select="system-property('xsl:product-version')"/>
</xsl:if>