Allow to use cmake to generate T tracer programs

- Add CMakeLists.txt to build all T tracer user tools
- Previous Makefiles are retained in common/utils/T: you can do
  $ cd common/utils/T/tracer
  $ make # all executables are there
  or also
  $ mkdir build && cd build
  $ cmake .. -GNinja
  $ ninja T_tools # all executables are in build/common/utils/T/tracer

common/utils/T/tracer/gui/CMakeLists.txt

@@ -0,0 +1,10 @@
+include(FindPkgConfig)
+pkg_check_modules(xft REQUIRED xft)
+find_library(X11 X11 REQUIRED)
+add_library(tracer_gui STATIC
+            init.c loop.c toplevel_window.c x.c container.c widget.c
+            gui.c label.c textarea.c event.c xy_plot.c textlist.c notify.c
+            positioner.c timeline.c space.c image.c)
+
+target_link_libraries(tracer_gui PRIVATE pthread m ${xft_LIBRARIES} X11)
+target_include_directories(tracer_gui PRIVATE ${xft_INCLUDE_DIRS})

common/utils/T/tracer/gui/x_defs.h

@@ -2,7 +2,7 @@
 #define _X_DEFS_H_
 
 #include <X11/Xlib.h>
-#include <Xft.h>
+#include <X11/Xft/Xft.h>
 
 struct x_connection {
   Display *d;