More distro friendly cmake fixes.

[cbalint13]

(x ) This PR address few issues:

1. Fix and advertise the optional SLANG_LIB_NAME for either STATIC or SHARED (see #650).
2. Fix SHARED mode, add PIC related flags and condition library visibility settings.
3. Automate adding of needed stdc++fs / c++fs variants for various compiler needs.

(x) This PR preserves and does not affect current build behaviour.

Cc: @jrudess

---

(x) See the introduced advertisements:

%cmake .. -Wno-dev \
       -DCMAKE_SKIP_RPATH=ON \
       -DCMAKE_VERBOSE_MAKEFILE=OFF \
       -DCMAKE_BUILD_TYPE=RelWithDebInfo \
       -DBUILD_SHARED_LIB=ON \
       -DSLANG_LIB_NAME="svlang" \
       -DSLANG_INCLUDE_LLVM=OFF \
       -DSLANG_INCLUDE_DOCS=OFF \
       -DSLANG_INCLUDE_TESTS=ON \
       -DSLANG_INCLUDE_PYLIB=ON \
       -DSLANG_INCLUDE_TOOLS=ON \
       -DSLANG_INCLUDE_INSTALL=ON
-- CMake version: 3.20.2
-- slang version: 2.0.0+211ccf5
-- The CXX compiler identification is GNU 8.5.0
{...}
-- Linking with: stdc++fs
-- Build SHARED library as: svlang
{..}

(x) Builds pass on {x86_64, ppc64le, aarch64} x {rhel8, rhel9, fc35, fc36, fc37, fc38}, see:
https://copr.fedorainfracloud.org/coprs/rezso/HDL/build/5034654/

---

@MikePopoloski,

Thank you for having this excellent tool !
~Cristian.

[codecov]

Codecov Report

Merging #655 (37c9a6b) into master (211ccf5) will increase coverage by 0.01%.
The diff coverage is n/a.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #655      +/-   ##
==========================================
+ Coverage   91.30%   91.31%   +0.01%     
==========================================
  Files         185      185              
  Lines       42677    42690      +13     
==========================================
+ Hits        38967    38984      +17     
+ Misses       3710     3706       -4     

Impacted Files	Coverage Δ
source/ast/symbols/PortSymbols.cpp	96.72% <0.00%> (ø)
include/slang/ast/symbols/InstanceSymbols.h	100.00% <0.00%> (ø)
source/driver/Driver.cpp	98.88% <0.00%> (+<0.01%)	⬆️
source/ast/symbols/InstanceSymbols.cpp	85.46% <0.00%> (+0.81%)	⬆️

---

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[MikePopoloski]

Do you have an example compiler where this is still needed? Note that slang does not build with a pre-C++17 compiler, and the minimum supported gcc version is 9 (and clang is 10) neither of which need the separate lib. In a few months I will bump the minimum gcc version to 10 and start requiring C++20 support so I'm wondering if there's some old system that will be broken if not supporting an older version.

[cbalint13]

• Yes, RHEL 8 (having gcc 8.x ) will fail without this.
• Not tested (myself) with other combinations outside fedora/rhel products.

A well proven routine is used from pybind11 library.

[MikePopoloski]

OK, I can merge this for now, but please be aware that I don't have the ability to maintain the codebase for very old compilers and so the build may or may not work for GCC 8 (and as mentioned I will be raising the minimum required C++ version to 20 early in 2023) and may be broken by any future changes that I make. Even the GCC team does not support GCC 8 anymore.

[cbalint13]

• Currently rhel8 is fine, in case you start require c++20, that's it, will drop out rhel8 support.
• There would be still some releng way to invoke gcc 10 even on RHEL 8, will update packaging at that time.

If interested in rhel/fedora native repo having sv-lang the automated (weekly) builds are here .

[MikePopoloski]

lgtm, thanks a lot for the PR!

[cbalint13]

lgtm, thanks a lot for the PR!

Also, thank you for your patience !
~Cristian.