VS2019加入VC-LTL编译Qt5.12.8去除VC运行时，支持WebEngine

由于QWebEngine只支持VS编译，在程序发布时各种VC运行时真的让人很崩溃，感谢初雨开源的VC_LTL让我们从VC运行时解脱出来。记录一下编译过程。
1.编译环境：
Windows10x64+VS2019社区版+Python2.7+Perl5.28.1+Ruby2.6.3+LLVM6.0; Qt5.12.8+ICU4C66+OpenSSl1.1.1d+VC-LTL4.1.0.2
2.编译脚本：

@echo off

REM Set up \Microsoft Visual Studio 2015, where <arch> is \c amd64, \c x86, etc.
REM CALL "D:\Application\Microsoft Visual Studio\2019\Community\VC\Auxiliary\Build\vcvars32.bat"
CALL "D:\Application\Microsoft Visual Studio\2019\Community\VC\Auxiliary\Build\vcvarsamd64_x86.bat"

REM Edit this location to point to the source code of Qt
SET _ROOT=F:\qt-everywhere-src-5.12.8

SET PATH=%_ROOT%\qtbase\bin;%_ROOT%\gnuwin32\bin;%PATH%

REM Uncomment the below line when using a git checkout of the source repository
SET PATH=%_ROOT%\qtrepotools\bin;%PATH%

REM Uncomment the below line when building with OpenSSL enabled. If so, make sure the directory points
REM to the correct location (binaries for OpenSSL).
SET PATH=D:\QtDevKit\VS2019_VC_LTL_x86_OpenSSL\bin;%PATH%

REM When compiling with ICU, uncomment the lines below and change <icupath> appropriately:
SET INCLUDE=D:\QtDevKit\VS2019_VC_LTL_x86_ICU4C66\include;%INCLUDE%
SET LIB=D:\QtDevKit\VS2019_VC_LTL_x86_ICU4C66\lib;%LIB%
SET PATH=D:\QtDevKit\VS2019_VC_LTL_x86_ICU4C66\lib;%PATH%
SET PATH=D:\QtDevKit\VS2019_VC_LTL_x86_ICU4C66\bin;%PATH%

REM LLVM
SET LLVM_INSTALL_DIR=C:\Program Files\LLVM
SET PATH=C:\Program Files\LLVM\bin;%PATH%
REM Contrary to earlier recommendations, do NOT set QMAKESPEC.

CD /D %_ROOT%

REM call configure -prefix D:\QtDevKit\VS2019_VC-LTL_x86_Qt5.12.8_NoOpenGl -opensource -release -mp -nomake tests -nomake examples -platform win32-msvc -openssl-linked -ID:\QtDevKit\VS2019_VC_LTL_x86_OpenSSL\include -LD:\QtDevKit\VS2019_VC_LTL_x86_OpenSSL\lib OPENSSL_LIBS="-llibssl -llibcrypto" -ID:\QtDevKit\VS2019_VC_LTL_x86_ICU4C66\include -LD:\QtDevKit\VS2019_VC_LTL_x86_ICU4C66\lib -icu

REM VC-LTL
REM qtbase\mkspecs\common\msvc-desktop.conf   MD -> MT
SET PATH=D:\QtDevKit\VC_LTL4.1.0.2\Redist\x86;%PATH%
CALL "D:\QtDevKit\VC_LTL4.1.0.2\VC-LTL helper for nmake.cmd"

REM Keeps the command line open when this script is run.
cmd /k

3.开始编译：
为了彻底摆脱VC运行时，首先编译ICU及OpenSSL;执行上面脚本（已加入VC-LTL），以MT方式编译完成就行。
修改QT文件：

	\qtbase\mkspecs\common\msvc-desktop.conf，从MD改为MT

QMAKE_CFLAGS_RELEASE    = $$QMAKE_CFLAGS_OPTIMIZE -MT
QMAKE_CFLAGS_RELEASE_WITH_DEBUGINFO += $$QMAKE_CFLAGS_OPTIMIZE -Zi -MT
QMAKE_CFLAGS_DEBUG      = -Zi -MTd

	\qtwebengine\src\3rdparty\chromium\build\config\win\BUILD.gn，从MD改为MT

config("release_crt") {
  if (is_component_build) {
    cflags = [ "/MT" ]
  } else {
    cflags = [ "/MT" ]
  }
}

config("dynamic_crt") {
  if (is_debug) {
    # This pulls in the DLL debug CRT and defines _DEBUG
    cflags = [ "/MTd" ]
  } else {
    cflags = [ "/MT" ]
  }
}

config("static_crt") {
  if (is_debug) {
    # This pulls in the static debug CRT and defines _DEBUG
    cflags = [ "/MTd" ]
  } else {
    cflags = [ "/MT" ]
  }
}

配置Qt编译过程，重点说明：（如是目标布署机器显卡老旧或不支持opengl，加上-no-opengl，否则在使用wegenginewidget时会黑屏等异常情况）

configure -prefix D:\QtDevKit\VS2019_VC-LTL_x86_Qt5.12.8_NoOpenGl -opensource -release -mp -nomake tests -nomake examples -platform win32-msvc -openssl-linked -ID:\QtDevKit\VS2019_VC_LTL_x86_OpenSSL\include -LD:\QtDevKit\VS2019_VC_LTL_x86_OpenSSL\lib OPENSSL_LIBS="-llibssl -llibcrypto" -ID:\QtDevKit\VS2019_VC_LTL_x86_ICU4C66\include -LD:\QtDevKit\VS2019_VC_LTL_x86_ICU4C66\lib -icu -no-opengl