Rename the VS2015 directory to VS2019, since we now build the Windows libraries using VS 2019. (#237)

* Rename the Windows packaged library directory to VS2019 since we now build using Visual Studio 2019.

* Add readme note about Windows directory change (and previous Linux
directory change) and new minimum VS version.

Author: jonsimantov

build_scripts/desktop/get_variant.sh

@@ -30,11 +30,11 @@ arch=
 arch_win=
 debugmode=Release
 msvc_runtime_library=MD
-vs=VS2015
+vs=VS2019
 stl=c++
 linux_abi=legacy
 
-for c in $(echo "${filename}" | tr "_.-" "\n\n\n"); do
+for c in $(echo "${filename}" | tr "[:upper:]" "[:lower:]" | tr "_.-" "\n\n\n"); do
     case $c in
 	# Operating systems
 	ios)
@@ -115,15 +115,9 @@ for c in $(echo "${filename}" | tr "_.-" "\n\n\n"); do
 	release)
 	    debugmode=Release
 	;;
-	Release)
-	    debugmode=Release
-	;;
 	debug)
 	    debugmode=Debug
 	;;
-	Debug)
-	    debugmode=Debug
-	;;
 	# Android STL variant
 	c++)
 	    stl=c++
@@ -143,6 +137,18 @@ for c in $(echo "${filename}" | tr "_.-" "\n\n\n"); do
 	legacy)
 	    linux_abi=legacy
         ;;
+	vs2019)
+	    vs=VS2019
+        ;;
+	vs2017)
+	    vs=VS2017
+        ;;
+	vs2015)
+	    vs=VS2015
+        ;;
+	vs2013)
+	    vs=VS2013
+        ;;
     esac
 done
 

release_build_files/CMakeLists.txt

@@ -45,7 +45,7 @@ elseif(MSVC)
   else()
     set(MSVC_CONFIG Debug)
   endif()
-  set(MSVC_VS_VERSION VS2015)
+  set(MSVC_VS_VERSION VS2019)
   set(FIREBASE_SDK_LIBDIR
       ${FIREBASE_CPP_SDK_DIR}/libs/windows/${MSVC_VS_VERSION}/${MSVC_RUNTIME_MODE}/${MSVC_CPU}/${MSVC_CONFIG})
 else()

release_build_files/readme.md

@@ -413,7 +413,7 @@ Firebase Instance ID (stub)     | firebase_instance_id.lib
 Firebase Cloud Messaging (stub) | firebase_messaging.lib
                                 | firebase_app.lib
 
-The provided libraries have been tested using Visual Studio 2015 and 2017. When
+The provided libraries have been tested using Visual Studio 2019. When
 building C++ desktop apps on Windows, you will need to link the following
 Windows SDK libraries (consult your compiler documentation for more
 information):
@@ -562,6 +562,15 @@ code.
 ### 7.0.0
 -   Changes
     -   General (iOS): iOS SDKs are now built using Xcode 11.7.
+    -   General (Desktop): Windows libraries are now built using Visual
+        Studio 2019. While VS 2019 is binary-compatible with VS 2015 and
+        VS 2017, you must use VS 2019 or newer to link the desktop SDK.
+        The libraries have been moved from libs/windows/VS2015 to
+        libs/windows/VS2019 to reflect this.
+    -   General (Desktop): Linux libraries are now built with both the
+        C++11 ABI and the legacy ABI. The libraries have been moved
+        from libs/linux/${arch} to libs/linux/${arch}/legacy and
+        libs/linux/${arch}/cxx11 to reflect this.
     -   AdMob (Android): Fix a JNI error when initializing without Firebase App.
     -   Analytics: Remove deprecated SetMinimumSessionDuration call.
     -   Installations: Added Installations SDK. See [Documentations](http://firebase.google.com/docs/reference/cpp/namespace/firebase/installations) for