[libxlsxwriter] Don't use PkgConfig

[dg0yt]

Fixes #43653.
Alternative to #43655.

[WangWeiLin-MV]

The port fix tests pass with the following triplets:

• x64-windows

[BillyONeal]

Thanks for the fix!

[jmcnamara]

Is this a fix that should be upstream in libxlsxwriter? I am the author/maintainer.

[WangWeiLin-MV]

Is this a fix that should be upstream in libxlsxwriter?

This PR is a workaround to fix by disable PKGConfig.

Could you mind look at a fix in another PR? #43655

[dg0yt]

You probably need to look at the problem (#43653), not at this PR.

IMO jmcnamara/libxlsxwriter@d963343 introduced problems:

• unexpectedly gave preference to pkg-config,
• uses raw <Pkg>_LDFLAGS when available.

This breaks MSVC toolchains. pkg-config and CMake can play together even for MSVC (with some CMake quirks left), but you cannot use raw LDFLAGS because pc files usually carry them in non-MSVC syntax. <Pkg>_LIBRARIES might be okay, or <Pkg>_LINK_LIBRARIES.

That change has another "unusual" (if not wrong) pattern, using else(<Condition>). It is probably meant to mean to be elseif(<Condition>).

[jmcnamara]

IMO jmcnamara/libxlsxwriter@d963343 introduced problems:

Thanks for that information. In that case I may revert the pkg-config change in libxlsxwriter. I'll look into it.