Fixed build on glibc systems

meson.build

@@ -1,6 +1,10 @@
 project('megapixels', 'c')
 gtkdep = dependency('gtk+-3.0')
-executable('megapixels', 'main.c', 'ini.c', 'bayer.c', dependencies : gtkdep, install : true)
+
+cc = meson.get_compiler('c')
+libm = cc.find_library('m', required: false)
+
+executable('megapixels', 'main.c', 'ini.c', 'bayer.c', dependencies : [gtkdep, libm], install : true)
 
 install_data(['camera.glade', 'camera.css'],
              install_dir : get_option('datadir') / 'megapixels/ui')