CMake updates for VS2015/cmake 3.12 onwards

cmake 3.12 adds MSVC_TOOLSET_VERSION to define the version of MSVC toolchain in use
Use that if present instead of if-elseif chain

CMakeLists.txt

@@ -106,7 +106,7 @@ OPTION ( BUILD_DOCS
   OFF
 )
 OPTION( INJECT_DEBUG_POSTFIX
-  "Inject debug postfix in .a/.so lib names"
+  "Inject debug postfix in .a/.so/.dll lib names"
   ON
 )
 
@@ -127,14 +127,15 @@ if (WIN32)
   ADD_DEFINITIONS( -DWIN32_LEAN_AND_MEAN )
 endif()
 
-
 IF(MSVC)
   OPTION( ASSIMP_INSTALL_PDB
     "Install MSVC debug files."
     ON
   )
-  # Multibyte character set is deprecated, but default
-  ADD_DEFINITIONS( -DUNICODE -D_UNICODE )
+  IF(NOT (MSVC_VERSION LESS 1900))
+    # Multibyte character set is deprecated since at least MSVC2015 (possibly earlier)
+    ADD_DEFINITIONS( -DUNICODE -D_UNICODE )
+  ENDIF()
 ENDIF(MSVC)
 
 IF (BUILD_FRAMEWORK)
@@ -545,18 +546,22 @@ if(WIN32)
   if (CMAKE_SIZEOF_VOID_P EQUAL 8)
     SET(BIN_DIR "${PROJECT_SOURCE_DIR}/bin64/")
     SET(LIB_DIR "${PROJECT_SOURCE_DIR}/lib64/")
-  elseif()
+  else()
     SET(BIN_DIR "${PROJECT_SOURCE_DIR}/bin32/")
     SET(LIB_DIR "${PROJECT_SOURCE_DIR}/lib32/")
   ENDIF()
 
-  IF(MSVC12)
-    SET(ASSIMP_MSVC_VERSION "vc120")
-  ELSEIF(MSVC14)
-    SET(ASSIMP_MSVC_VERSION "vc140")
-  ELSEIF(MSVC15)
-    SET(ASSIMP_MSVC_VERSION "vc141")
-  ENDIF(MSVC12)
+  IF(MSVC_TOOLSET_VERSION)
+    set(MSVC_PREFIX "vc${MSVC_TOOLSET_VERSION}")
+  ELSE()
+    IF(MSVC12)
+      SET(ASSIMP_MSVC_VERSION "vc120")
+    ELSEIF(MSVC14)
+      SET(ASSIMP_MSVC_VERSION "vc140")
+    ELSEIF(MSVC15)
+      SET(ASSIMP_MSVC_VERSION "vc141")
+    ENDIF(MSVC12)
+  ENDIF()
 
   IF(MSVC12 OR MSVC14 OR MSVC15 )
     ADD_CUSTOM_TARGET(UpdateAssimpLibsDebugSymbolsAndDLLs COMMENT "Copying Assimp Libraries ..." VERBATIM)

code/CMakeLists.txt

@@ -1037,6 +1037,10 @@ ENDIF (ASSIMP_BUILD_NONFREE_C4D_IMPORTER)
 
 if( MSVC )
   # in order to prevent DLL hell, each of the DLLs have to be suffixed with the major version and msvc prefix
+  # CMake 3.12 added a variable for this
+  if(MSVC_TOOLSET_VERSION)
+    set(MSVC_PREFIX "vc${MSVC_TOOLSET_VERSION}")
+  else()
   if( MSVC70 OR MSVC71 )
     set(MSVC_PREFIX "vc70")
   elseif( MSVC80 )
@@ -1051,9 +1055,12 @@ if( MSVC )
     set(MSVC_PREFIX "vc120")
   elseif( MSVC14 )
     set(MSVC_PREFIX "vc140")
+  elseif( MSVC15 )
+    set(MSVC_PREFIX "vc141")
   else()
     set(MSVC_PREFIX "vc150")
   endif()
+  endif()
   set(LIBRARY_SUFFIX "${ASSIMP_LIBRARY_SUFFIX}-${MSVC_PREFIX}-mt" CACHE STRING "the suffix for the assimp windows library")
 endif()