[tracker] meson: Allow to build with non-GNU libc

[Sam Thursfield <sthursfield src gnome org>]

commit 19443a0f71d9bd9793b40f7be4c4879e88de7ecc
Author: Quentin Glidic <sardemff7+git sardemff7 net>
Date:   Sun Dec 10 11:17:41 2017 +0100

    meson: Allow to build with non-GNU libc
    
    https://bugzilla.gnome.org/show_bug.cgi?id=791432
    
    Signed-off-by: Quentin Glidic <sardemff7+git sardemff7 net>

 meson.build |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/meson.build b/meson.build
index 8a159af..e293215 100644
--- a/meson.build
+++ b/meson.build
@@ -31,7 +31,7 @@ libxml2 = dependency('libxml-2.0', version: '> 2.6')
 network_manager = dependency('libnm', required: false)
 sqlite = dependency('sqlite3', version: '>' + sqlite_required)
 
-libmath = cc.find_library('m')
+libmath = cc.find_library('m', required: false)
 
 # FIXME: here we work around a quirk todo with Meson and Vala: the 'uuid'
 # pkg-config component corresponds to 'libuuid.vapi', but Meson assumes that