Always use 19.20 (Visual Studio 16 2019) for now

cpp/src/gandiva/precompiled/CMakeLists.txt

@@ -30,25 +30,17 @@ set(PRECOMPILED_SRCS
     timestamp_arithmetic.cc
     ../../arrow/util/basic_decimal.cc)
 
+set(PLATFORM_CLANG_OPTIONS -std=c++17)
 if(MSVC)
-  # clang pretends to be a particular version of MSVC. The standard
-  # library uses C++14 features, so we have to use that -std version
-  # to get the IR compilation to work.
+  # "19.20" means that it's compatible with Visual Studio 16 2019.
+  # We can update this to "19.30" when we dropped support for Visual
+  # Studio 16 2019.
+  #
   # See https://cmake.org/cmake/help/latest/variable/MSVC_VERSION.html
   # for MSVC_VERSION and Visual Studio version.
-  if(MSVC_VERSION LESS 1920)
-    set(FMS_COMPATIBILITY 19.10)
-  elseif(MSVC_VERSION LESS 1930)
-    set(FMS_COMPATIBILITY 19.20)
-  elseif(MSVC_VERSION LESS 1940)
-    set(FMS_COMPATIBILITY 19.30)
-  else()
-    message(FATAL_ERROR "Unsupported MSVC_VERSION=${MSVC_VERSION}")
-  endif()
-  set(PLATFORM_CLANG_OPTIONS -std=c++17 -fms-compatibility
-                             -fms-compatibility-version=${FMS_COMPATIBILITY})
-else()
-  set(PLATFORM_CLANG_OPTIONS -std=c++17)
+  set(FMS_COMPATIBILITY 19.20)
+  list(APPEND PLATFORM_CLANG_OPTIONS -fms-compatibility
+       -fms-compatibility-version=${FMS_COMPATIBILITY})
 endif()
 
 # Create bitcode for each of the source files.