reorganize cmake in small scripts with some fix from https://github.com/cnjinhao/nana/pull/278

build/cmake/compilers.cmake

@@ -0,0 +1,48 @@
+
+########### Compilers
+#
+# Using gcc: gcc 4.8 don't support C++14 and make_unique. You may want to update at least to 4.9.
+# gcc 5.3 and 5.4 include filesytem, but you need to add the link flag: -lstdc++fs
+#
+# In Windows, with CLion Allways check in File/Settings.../toolchains
+# You could install MinGW-w64 from the TDM-GCC Compiler Suite for Windows which will update you to gcc 5.1.
+# It is posible to follow https://computingabdn.com/softech/mingw-howto-install-gcc-for-windows/
+# and install MinGW with gcc 7.1 with has STD_THREADS and fs, from: https://sourceforge.net/projects/mingw-w64/files/
+#
+# see at end of:  https://gcc.gnu.org/onlinedocs/libstdc++/manual/using_dynamic_or_shared.html
+#
+
+if(CMAKE_COMPILER_IS_GNUCXX OR "${CMAKE_CXX_COMPILER_ID}" MATCHES "Clang") #  AND NOT MINGW??
+
+    target_compile_options(nana PRIVATE  -Wall
+                                 PUBLIC  -g   )
+
+    set(THREADS_PREFER_PTHREAD_FLAG ON)               #  todo - test this
+    find_package(Threads REQUIRED)
+    target_link_libraries(nana PRIVATE Threads::Threads)
+    #    target_compile_options(nana PUBLIC -pthread)
+
+
+    if("${CMAKE_CXX_COMPILER_ID}" MATCHES "Clang")
+        if("${CMAKE_SYSTEM_NAME}" MATCHES "FreeBSD")
+            target_compile_options(nana PUBLIC -I/usr/local/include)
+        endif()
+    endif()
+
+
+    # target_link_libraries(nana PRIVATE stdc++fs)    # ??
+
+
+endif()
+
+
+if (APPLE AND "${CMAKE_CXX_COMPILER_ID}" MATCHES "Clang")                    # APPLE Clang
+    target_compile_options(nana PUBLIC -stdlib=libstdc++)
+endif ()
+
+
+
+if("${CMAKE_CXX_COMPILER_ID}" MATCHES "GNU")
+    target_compile_options(nana PRIVATE -fmax-errors=3)
+endif()
+