libxslt: Fix build
libxslt: Fix build

Fixes:
2021-05-25T19:32:46.5378757Z checking for xml2-config... /home/linuxbrew/.linuxbrew/opt/libxml2/bin/xml2-config
2021-05-25T19:32:46.5380027Z ./configure: line 15402: syntax error near unexpected token `LIBXML,'
2021-05-25T19:32:46.5381168Z ./configure: line 15402: `        PKG_CHECK_MODULES(LIBXML, libxml-2.0 >= $LIBXML_REQUIRED_VERSION,'

Closes #23313.

Signed-off-by: Michka Popoff <5d406f95fb0e0230f83654e4a22d0115cc205d59@users.noreply.github.com>

Linuxbrew/homebrew-core,Linuxbrew/homebrew-core