Added a feature test to auto enable/disable CPPHTTPLIB_USE_NON_BLOCKI…

[TobiasWallner]

Summary

Add CMake feature detection for CPPHTTPLIB_USE_NON_BLOCKING_GETADDRINFO on Windows.

When HTTPLIB_USE_NON_BLOCKING_GETADDRINFO is enabled, CMake now checks whether GetAddrInfoExCancel is available before exporting CPPHTTPLIB_USE_NON_BLOCKING_GETADDRINFO through the httplib::httplib target. If the symbol is not available, the non-blocking getaddrinfo support is disabled automatically.

Motivation

Some Windows machines/toolchains do not provide GetAddrInfoExCancel, which causes downstream projects using cpp-httplib via CMake to fail compilation when CPPHTTPLIB_USE_NON_BLOCKING_GETADDRINFO is exported unconditionally.

Previously, consumers had to work around this by manually removing the interface compile definition from httplib::httplib. With this change, cpp-httplib configures itself correctly out of the box.

Testing

Verified on a Windows machine where GetAddrInfoExCancel is unavailable:

• CMake reports GetAddrInfoExCancel - not found
• HTTPLIB_IS_USING_NON_BLOCKING_GETADDRINFO is set to FALSE
• CPPHTTPLIB_USE_NON_BLOCKING_GETADDRINFO is not present on the consumer compile line
• compiled-library mode builds successfully

[yhirose]

@sum01 @jimmy-park @Tachi107 this PR looks good to me. Could you please take a look at it?

[yhirose]

@TobiasWallner could you take a look at the CI failures of test / windows with SSL and test /windows without SSL? (You don't need to worry about other failures.)