libmicrohttpd: several fixes & more conan v2 stuff

[SpaceIm]

• relocatable shared lib on macOS
• put source code under src folder
• use rm_safe
• delete fPIC option if Windows only
• allow other build type than Release & Debug for msvc
• add VirtualBuildEnv for autotools build (since there is msys2 in build requirements for MinGW)
• use AutotoolsDeps to be sure to find zlib
• remove PkgConfigDeps. It's used to discover gnutls only, but it's disabled by the recipe currently.
• more future proof way to use MSBuild helper (see MSBuild: add argument to build() to opt-in autoconsumption of props files generated by MSBuildToolchain & MSBuildDeps conan#12817)
• disable whole program optimization in msvc build

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• I've read the contributing guidelines.
• I've used a recent Conan client version close to the currently deployed.
• I've tried at least one configuration locally with the conan-center hook activated.

[conan-center-bot]

Conan v1 pipeline

All green in build 5 (0f07a4530b55411e732ec7ebb54f0918c3ec3146):

• libmicrohttpd/0.9.75@:
  All packages built successfully! (All logs)

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Conan v2 pipeline (informative, not required for merge)

Failure in build 5 (0f07a4530b55411e732ec7ebb54f0918c3ec3146):

• libmicrohttpd/0.9.75@:
  CI failed to create some packages (All logs)

  Logs for packageID null:

  [settings]
  arch=x86_64
  build_type=Release
  compiler=gcc
  compiler.libcxx=libstdc++11
  compiler.version=11
  os=Linux
  [options]
  */*:shared=False
  

  ********************************************************************************
  conan install --require=libmicrohttpd/0.9.75@#67ad0c03b601705ca9acbb1bf9156e73 --build=libmicrohttpd/0.9.75 -pr:h /home/conan/w/prod-v2/BuildSingleReference/9429/a45913e0-5cf6-4de6-b970-8b85434e3800/profile_linux_11_libstdcpp11_gcc_release_64.-shared-False.txt -c:h tools.system.package_manager:mode=install -c:h tools.system.package_manager:sudo=True -pr:b /home/conan/w/prod-v2/BuildSingleReference/9429/a45913e0-5cf6-4de6-b970-8b85434e3800/profile_linux_11_libstdcpp11_gcc_release_64.-shared-False.txt -c:b tools.system.package_manager:mode=install -c:b tools.system.package_manager:sudo=True
  ********************************************************************************
  
  -------- Input profiles --------
  Profile host:
  [settings]
  arch=x86_64
  build_type=Release
  compiler=gcc
  compiler.libcxx=libstdc++11
  compiler.version=11
  os=Linux
  [options]
  */*:shared=False
  [conf]
  tools.system.package_manager:mode=install
  tools.system.package_manager:sudo=True
  
  Profile build:
  [settings]
  arch=x86_64
  build_type=Release
  compiler=gcc
  compiler.libcxx=libstdc++11
  compiler.version=11
  os=Linux
  [options]
  */*:shared=False
  [conf]
  tools.system.package_manager:mode=install
  tools.system.package_manager:sudo=True
  
  
  -------- Computing dependency graph --------
  zlib/1.2.13: Not found in local cache, looking in remotes...
  zlib/1.2.13: Checking remote: conan-center-v2
  zlib/1.2.13: Checking remote: c3i_PR-v2-15050
  Graph root
      virtual
  Requirements
      libmicrohttpd/0.9.75#67ad0c03b601705ca9acbb1bf9156e73 - Cache
  Graph error
      Package 'zlib/1.2.13' not resolved: Unable to find 'zlib/1.2.13' in remotes
  
  -------- Computing necessary packages --------
  ERROR: Package 'zlib/1.2.13' not resolved: Unable to find 'zlib/1.2.13' in remotes
  

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