[gdk-pixbuf] Put back the round and lrint checks

[Emmanuele Bassi <ebassi src gnome org>]

commit a78ccf6b7705a8dd0ffbf724c1184b6b5103b4ae
Author: Emmanuele Bassi <ebassi gnome org>
Date:   Tue Aug 1 16:06:13 2017 +0100

    Put back the round and lrint checks
    
    We depend on C99 functions in the math library; if the math library is
    not found, or if it's not C99-compliant, we have fallbacks in place.
    
    Commit 68da550e817b1269d1ccfdeeec2a53ddbd7b920a removed the checks, and
    we ended up compiling the fallbacks even when the C library provided
    these symbols — leading to a build error caught by Continuous.

 configure.ac |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index 4637188..01438d1 100644
--- a/configure.ac
+++ b/configure.ac
@@ -96,8 +96,11 @@ PKG_PROG_PKG_CONFIG
 
 AC_CANONICAL_HOST
 
+# Check for libm and look for these C99 functions
 AC_CHECK_LIBM
 AC_SUBST(LIBM)
+AC_CHECK_LIB(m, round, AC_DEFINE(HAVE_ROUND, [1], [Define to 1 if libm has round]))
+AC_CHECK_LIB(m, lrint, AC_DEFINE(HAVE_LRINT, [1], [Define to 1 if libm has lrint]))
 
 AC_MSG_CHECKING([for native Win32])
 LIB_EXE_MACHINE_FLAG=X86