[libgxps] meson: libm should not be required

[Ignacio Casal Quinteiro <icq src gnome org>]

commit 589a799e594bac34b0bafa0712e2d78f6e512810
Author: Danny 'Guru' Forghieri <daniele forghieri gmail com>
Date:   Fri Sep 8 00:06:15 2017 +0200

    meson: libm should not be required
    
    There are some platforms like windows where there is no need
    to link to this library.

 meson.build |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/meson.build b/meson.build
index bcf32fc..1c7c2ef 100644
--- a/meson.build
+++ b/meson.build
@@ -153,7 +153,7 @@ cdata.set('HAVE_LIBJPEG', jpeg_dep.found())
 cdata.set('HAVE_LIBTIFF', tiff_dep.found())
 
 # Maths functions might be implemented in libm
-libm_dep = cc.find_library('m')
+libm_dep = cc.find_library('m', required: false)
 
 gnome = import('gnome')
 gir = find_program('g-ir-scanner', required: false)