1. Check system integrity
I do not see GLib-CRITICAL messages on my systems, so if unsure, then reinstall related packages with:
sudo apt-get install --reinstall libglib2.0-0 libglib2.0-bin libglib2.0-data
If problem persists, then check system integrity with:
sudo dpkg --verify
or debsums:
sudo apt-get install debsums
sudo debsums --all --changed
and reinstall packages with possible damaged/missed/changed files.
2. Install packages with *.pc files
About *.pc files. If you visit search on https://packages.ubuntu.com and evaluate search for *.pc files inside packages you will see the long list of related packages and files:

So you need to install some related dev-packages.
At least one libglib2.0-dev with glib-2.0.pc:
sudo apt-get install libglib2.0-dev
and you will get something like:
$ pkg-config --list-all | grep -A2 -B2 GLib
iso-codes iso-codes - ISO country, language, script and currency codes and translations
caja-python Caja-Python - Caja-Python Components
gobject-2.0 GObject - GLib Type, Object, Parameter and Signal Library
gmodule-export-2.0 GModule - Dynamic module loader for GLib
libpcreposix libpcreposix - PCREPosix - Posix compatible interface to libpcre
geoclue-2.0 Geoclue - The Geoinformation Service
--
adwaita-icon-theme gnome-icon-theme - A collection of icons used as the basis for GNOME themes
libpcre libpcre - PCRE - Perl compatible regular expressions C library with 8 bit character support
glib-2.0 GLib - C Utility Library
mate-keybindings mate-keybindings - Keybindings configuration for MATE applications
gmodule-2.0 GModule - Dynamic module loader for GLib
gnome-system-tools gst - Gnome System Tools
gthread-2.0 GThread - Thread support for GLib
caja-sendto caja-sendto - Extend caja-sendto through plugins
xbitmaps X bitmaps - Bitmaps that are shared between X applications
--
libpcre32 libpcre32 - PCRE - Perl compatible regular expressions C library with 32 bit character support
xkeyboard-config XKeyboardConfig - X Keyboard configuration data
gmodule-no-export-2.0 GModule - Dynamic module loader for GLib
xkbcomp xkbcomp - XKB keymap compiler
(tested on clean Ubuntu 18.04.2 LTS virtual machine)
Note: Debian and Ubuntu are not source-based GNU/Linux distributions, i.e. they are not Gentoo or Funtoo. For latter it is expected to have includes and development packages and tools preinstalled, but for Debian it is not expected.