[LyX/2.3.x] endl needs ostream header here.

[Scott Kostyshak]

commit 6b4c7c5e9107716353f8c3315fe93abfc0a27c1a
Author: Pavel Sanda <sanda at lyx.org>
Date:   Tue Jan 14 21:59:05 2020 +0100

    endl needs ostream header here.
    
    (cherry picked from commit 8c4d6bbba68d0913ae4a7ec3beefea0e9ff4d8ea)
---
 src/boost.cpp |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)

diff --git a/src/boost.cpp b/src/boost.cpp
index ce1fb27..646d4e4 100644
--- a/src/boost.cpp
+++ b/src/boost.cpp
@@ -18,6 +18,7 @@
 
 #include <exception>
 #include <iomanip>
+#include <ostream>
 
 using namespace std;
 using lyx::lyxerr;