Fixes this issue:
 <https://github.com/mariusmuja/flann/issues/369>.
Patch from Buildroot:
 <https://github.com/buildroot/buildroot/commit/45a39b3e2ba42b72d19bfcef30db1b8da9ead51a>.

From fa5ec96a94646492a3f908e12905b3e48a8e800b Mon Sep 17 00:00:00 2001
From: Romain Naour <romain.naour@gmail.com>
Date: Wed, 18 Apr 2018 20:24:13 +0200
Subject: [PATCH] src/cpp: fix cmake >= 3.11 build

CMake < 3.11 doesn't support add_library() without any source file
(i.e add_library(foo SHARED)). But flann CMake use a trick that use
an empty string "" as source list (i.e add_library(foo SHARED "")).
This look like a bug in CMake < 3.11.

With CMake >= 3.11, the new behaviour of add_library() break the
existing flann CMake code.

From CMake Changelog [1]:
"add_library() and add_executable() commands can now be called without
 any sources and will not complain as long as sources are added later
 via the target_sources() command."

Note: flann CMake code doesn't use target_sources() since no source fil</td></tr></table>
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STREQUAL "Linux" AND CMAKE_COMPILER_IS_GNUCC)
-        add_library(flann SHARED "")
+        add_library(flann SHARED "empty.cpp")
         set_target_properties(flann PROPERTIES LINKER_LANGUAGE CXX)
         target_link_libraries(flann -Wl,-whole-archive flann_s -Wl,-no-whole-archive)
     else()
diff --git a/src/cpp/empty.cpp b/src/cpp/empty.cpp
new file mode 100644
index 0000000..40a8c17
--- /dev/null
+++ b/src/cpp/empty.cpp
@@ -0,0 +1 @@
+/* empty */
-- 
2.14.3