Configure script not picking up XFT for "anti aliased fonts"

[R. Diez]

Hi all:

I am upgrading to Emacs 27.1 on two similar PCs with Ubuntu 18.04.5 LTS.

On one of them, the configure script says (I added some empty lines):

  checking for fontconfig >= 2.2.0... yes

  checking for xft >= 0.13.0... yes
  checking for X11/Xft/Xft.h... yes
  checking for XftFontOpen in -lXft... yes
  checking for freetype2... yes

  checking for FT_Face_GetCharVariantIndex... yes

  [...]

  Does Emacs use -lxft?    yes


On the other computer, the xft lines in the middle are just missing:

  checking for fontconfig >= 2.2.0... yes

  checking for FT_Face_GetCharVariantIndex... yes

  [...]

  Does Emacs use -lxft?      no

I do not really know if this xft is needed nowadays.

I am configuring with "--with-x-toolkit=gtk3  --with-cairo  --with-xwidgets". 
All other detected configuration options are the same on both systems.

I tried forcing it by specifying --with-xft , but that does not make any difference. There is no indication about why the configure script is not 
probing for xft.

Both Emacs report the same system-configuration-features:

XPM JPEG TIFF GIF PNG RSVG CAIRO SOUND GPM DBUS GSETTINGS GLIB NOTIFY INOTIFY ACL LIBSELINUX GNUTLS LIBXML2 FREETYPE HARFBUZZ M17N_FLT LIBOTF ZLIB 
TOOLKIT_SCROLL_BARS GTK3 X11 XDBE XIM MODULES THREADS XWIDGETS LIBSYSTEMD JSON PDUMPER LCMS2 GMP

There is no visible difference. The fonts look the same as before with Emacs 
26.2 on both systems.

I searched for the Ubuntu/Debian package that provides Xft.h, and it is libxft-dev , which was already installed on the computer that is not picking 
up -lxft .

Can somebody shed some light on this?

Thanks in advance,
  rdiez