[LyX/master] Cmake build: Mimic changes done in autoconf at f70dd65

[Kornel Benko]

commit 396b55dd519eeef3701b0768c6f7e6a40eb2f6fe
Author: Kornel Benko <kor...@lyx.org>
Date:   Fri Jul 8 10:58:32 2016 +0200

    Cmake build: Mimic changes done in autoconf at f70dd65
---
 development/cmake/configCompiler.h.cmake |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)

diff --git a/development/cmake/configCompiler.h.cmake 
b/development/cmake/configCompiler.h.cmake
index 29ff199..52f629e 100644
--- a/development/cmake/configCompiler.h.cmake
+++ b/development/cmake/configCompiler.h.cmake
@@ -98,6 +98,7 @@
 #define BOOST_NO_WSTRING 1
 
 #ifdef __CYGWIN__
+#  define _DEFAULT_SOURCE
 #  define BOOST_POSIX 1
 #  define BOOST_POSIX_API 1
 #  define BOOST_POSIX_PATH 1