Option to NOT force libc++ when building with clang (#4826)

* Eclipse ignore

* TypeScript support

* Prefixing enums

* Test results

* Merged JS and TS generators

* Fixed AppVeyor build problems

* Fixed more AppVeyor build problems

* Fixed more AppVeyor build problems

* Changed TS flag to options struct

* Storing options by value

* Removed unneeded const

* Re-export support for unions

* Uint support

* Casting bools to numbers for mutation

* TS shell tests

* Reverted generates js test file to original version

* Backing up js tests and properly generating test data

* Not importing flatbuffers for TS test generation

* Not overwriting generated js for tests

* AppVeyor test fixes

* Generating the most strict TS code possible

* Not returning null when creating vectors

* Not returning null from struct contructors

* Vector of unions for ts/js

* Sanity check for languages

* Indentation fix + output test files

* Vectors of unions for php

* Fixes to union vector handling + tests

* Fix for strictPropertyInitialization

* Fix for new aligned operator new for gcc >= 7.1

* Not generating imports/ns prefixes with --gen-all

* TypeScript docs

* Missing imports of enums

* Missing TS links

* Enabled vector of unions for java, since it seems to work

* Added jitpack config

* Added obj to vector of unions getter

* Removed unneeded accessor

* Bumped jdk version in pom.xml

* Vector of unions support for c#

* Missing TypeScript doc processing

* Option to NOT force libc++ when building with clang

CMakeLists.txt

@@ -15,6 +15,7 @@ option(FLATBUFFERS_BUILD_GRPCTEST "Enable the build of grpctest" OFF)
 option(FLATBUFFERS_BUILD_SHAREDLIB
        "Enable the build of the flatbuffers shared library"
        OFF)
+option(FLATBUFFERS_LIBCXX_WITH_CLANG "Force libc++ when using Clang" ON)
 
 if(NOT FLATBUFFERS_BUILD_FLATC AND FLATBUFFERS_BUILD_TESTS)
     message(WARNING
@@ -139,14 +140,16 @@ elseif(CMAKE_COMPILER_IS_GNUCXX)
 elseif(${CMAKE_CXX_COMPILER_ID} MATCHES "Clang")
   set(CMAKE_CXX_FLAGS
       "${CMAKE_CXX_FLAGS} -std=c++0x -Wall -pedantic -Werror -Wextra -Wno-unused-parameter")
-  if(NOT "${CMAKE_SYSTEM_NAME}" MATCHES "Linux")
-    set(CMAKE_CXX_FLAGS
-        "${CMAKE_CXX_FLAGS} -stdlib=libc++")
-  endif()
-  if(NOT ("${CMAKE_SYSTEM_NAME}" MATCHES "FreeBSD" OR
-          "${CMAKE_SYSTEM_NAME}" MATCHES "Linux"))
-    set(CMAKE_EXE_LINKER_FLAGS
-        "${CMAKE_EXE_LINKER_FLAGS} -lc++abi")
+  if(FLATBUFFERS_LIBCXX_WITH_CLANG)
+    if(NOT "${CMAKE_SYSTEM_NAME}" MATCHES "Linux")
+      set(CMAKE_CXX_FLAGS
+          "${CMAKE_CXX_FLAGS} -stdlib=libc++")
+    endif()
+    if(NOT ("${CMAKE_SYSTEM_NAME}" MATCHES "FreeBSD" OR
+            "${CMAKE_SYSTEM_NAME}" MATCHES "Linux"))
+      set(CMAKE_EXE_LINKER_FLAGS
+          "${CMAKE_EXE_LINKER_FLAGS} -lc++abi")
+    endif()
   endif()
 
   # Certain platforms such as ARM do not use signed chars by default