[gimp/gimp-2-10] plug-ins: optionally define several float.h macros for MinGW64.

[Jehan <jehanp src gnome org>]

commit 69712634a134f720f7a49c4fe445da17a9bea7b3
Author: Jehan <jehan girinstud io>
Date:   Sat Jan 26 14:47:56 2019 +0100

    plug-ins: optionally define several float.h macros for MinGW64.
    
    This plug-in failed to cross-build because these macros were not defined
    in the `float.h` of my MinGW64 environment (and they are used in some
    ilmbase headers). Just define them ourselves if they are absent. I do
    this only on MinGW environment because these should really be defined on
    Linux (and other UNIX-like, I guess?) and if they are not, we may have a
    bigger issue.
    
    (cherry picked from commit 7a7ecda4f170b1fead91bcc53d014d47c563513e)

 plug-ins/file-exr/openexr-wrapper.cc | 12 ++++++++++++
 1 file changed, 12 insertions(+)
---
diff --git a/plug-ins/file-exr/openexr-wrapper.cc b/plug-ins/file-exr/openexr-wrapper.cc
index ef401f8daf..ff3e14d0c0 100644
--- a/plug-ins/file-exr/openexr-wrapper.cc
+++ b/plug-ins/file-exr/openexr-wrapper.cc
@@ -11,6 +11,18 @@
 
 #include "openexr-wrapper.h"
 
+#if defined(__MINGW32__)
+#ifndef FLT_EPSILON
+#define FLT_EPSILON  __FLT_EPSILON__
+#endif
+#ifndef DBL_EPSILON
+#define DBL_EPSILON  __DBL_EPSILON__
+#endif
+#ifndef LDBL_EPSILON
+#define LDBL_EPSILON __LDBL_EPSILON__
+#endif
+#endif
+
 #include <ImfInputFile.h>
 #include <ImfChannelList.h>
 #include <ImfRgbaFile.h>