Don't touch linker flags unless on MSVC

Change-Id: I07831de58b195cfb285c5c9170207bfff29e7516

Author: wesm

cpp/CMakeLists.txt

@@ -313,7 +313,7 @@ Note that this requires linking Boost statically"
   if (MSVC)
     option(MSVC_LINK_VERBOSE
       "Pass verbose linking options when linking libraries and executables"
-      on)
+      ON)
 
     option(ARROW_USE_CLCACHE
       "Use clcache if available"

cpp/cmake_modules/SetupCxxFlags.cmake

@@ -415,17 +415,16 @@ message(STATUS "Build Type: ${CMAKE_BUILD_TYPE}")
 # ----------------------------------------------------------------------
 # MSVC-specific linker options
 
-set(MSVC_LINKER_FLAGS)
-
-if (MSVC_LINK_VERBOSE)
-  set(MSVC_LINKER_FLAGS "${MSVC_LINKER_FLAGS} /VERBOSE:LIB")
+if (MSVC)
+  set(MSVC_LINKER_FLAGS)
+  if (MSVC_LINK_VERBOSE)
+    set(MSVC_LINKER_FLAGS "${MSVC_LINKER_FLAGS} /VERBOSE:LIB")
+  endif()
+  set(MSVC_LINKER_FLAGS "${MSVC_LINKER_FLAGS} /NODEFAULTLIB:LIBCMT")
+  set(CMAKE_EXE_LINKER_FLAGS
+    "${CMAKE_EXE_LINKER_FLAGS} ${MSVC_LINKER_FLAGS}")
+  set(CMAKE_MODULE_LINKER_FLAGS
+    "${CMAKE_MODULE_LINKER_FLAGS} ${MSVC_LINKER_FLAGS}")
+  set(CMAKE_SHARED_LINKER_FLAGS
+    "${CMAKE_SHARED_LINKER_FLAGS} ${MSVC_LINKER_FLAGS}")
 endif()
-
-set(MSVC_LINKER_FLAGS "${MSVC_LINKER_FLAGS} /NODEFAULTLIB:LIBCMT")
-
-set(CMAKE_EXE_LINKER_FLAGS
-  "${CMAKE_EXE_LINKER_FLAGS} ${MSVC_LINKER_FLAGS}")
-set(CMAKE_MODULE_LINKER_FLAGS
-  "${CMAKE_MODULE_LINKER_FLAGS} ${MSVC_LINKER_FLAGS}")
-set(CMAKE_SHARED_LINKER_FLAGS
-  "${CMAKE_SHARED_LINKER_FLAGS} ${MSVC_LINKER_FLAGS}")