build: Meson options for custom OpenSSL lib/hdr path

[win32asm]

Required in case the openssl library is not native to the build environment (e.g. part of vcpkg fetched dependencies).

[codecov[bot]]

Codecov Report

Patch coverage has no change and project coverage change: +0.10% :tada:

Comparison is base (fe5639a) 77.92% compared to head (373ca0f) 78.02%.

:exclamation: Current head 373ca0f differs from pull request most recent head 667be05. Consider uploading reports for the commit 667be05 to get more accurate results

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #1162 +/- ## ========================================== + Coverage 77.92% 78.02% +0.10% ========================================== Files 53 53 Lines 6990 6990 ========================================== + Hits 5447 5454 +7 + Misses 1543 1536 -7 ``` [see 3 files with indirect coverage changes](https://app.codecov.io/gh/pistacheio/pistache/pull/1162/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pistacheio)

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[kiplingw]

Thanks @win32asm. Can you also remember to document the proposed new build flags in our README.md?

[kiplingw]

I'm fine with it. @dennisjenkins75, @Tachi107?

[Tachi107]

I'm not a fan of this workaround. Can't you simply override the pkg-config search directories to include your custom OpenSSL build?

[win32asm]

I'm not a fan of this workaround. Can't you simply override the pkg-config search directories to include your custom OpenSSL build?

Let us see if we can use a pkg-config-based detection way.

[kiplingw]

I'm not a fan of this workaround. Can't you simply override the pkg-config search directories to include your custom OpenSSL build?

That's actually a really good point.

[win32asm]

Thanks for the idea.

We ended up doing

PKG_CONFIG_PATH=<openssl pvt build path>/lib/pkgconfig:${PKG_CONFIG_PATH} \
meson setup build ...

[Tachi107]

Nice to hear! Happy to help :)