Ending support for V8-enabled builds with MSVC

[Lei Zhang]

Hi,

V8 has decided to end support for MSVC [1] in a few months. PDFium will adjust accordingly as follows:

1) Change PDFium's MSVC continuous build bots to use a build configuration without V8 this week. [2]

2) Continue to support building V8-enabled PDFium with MSVC until September.

3) Stop supporting building V8-enabled PDFium with MSVC in September, once V8 has been updated to version 13.x.

Building PDFium without V8 using MSVC will still be supported at this time.

As previously mentioned [2], clang-cl built PDFium binaries should be ABI compatible with MSVC. If desired, one can build PDFium using clang-cl, and still use MSVC to build the rest of a project.

[1] https://groups.google.com/g/v8-dev/c/8mSxb2UriSU

[2] https://crbug.com/347647409

[3] https://groups.google.com/g/pdfium/c/d7KZi_wePHs/m/glNrV1S3BAAJ