[paho-mqttpp3] Add New Port: Paho MQTT C++ library (#7033)

* added port: paho-mqtt-cpp

* fixed unix build

* Added openssl as a feature

* Added documentation

* commented out unnecessary stuff

* Updated as per code review

* [paho-mqttpp3] Simplify portfile

ports/paho-mqttpp3/CONTROL

@@ -0,0 +1,9 @@
+Source: paho-mqttpp3
+Version: 1.0.1
+Description: Paho project provides open-source C++ wrapper for Paho C library
+Build-Depends: paho-mqtt
+Default-Features: ssl
+
+Feature: ssl
+Description: Build with SSL support
+Build-Depends: openssl

ports/paho-mqttpp3/portfile.cmake

@@ -0,0 +1,66 @@
+include(vcpkg_common_functions)
+
+# Download from Github
+vcpkg_from_github(
+  OUT_SOURCE_PATH SOURCE_PATH
+  REPO eclipse/paho.mqtt.cpp
+  REF v1.0.1
+  SHA512 be612197fae387b9f1d8f10944d451ec9e7ebec6045beed365e642089c0a5fde882ed5c734f2b46a5008f98b8445a51114492f0f36fdc684b8a8fe4b71fe31a4
+  HEAD_REF master
+)
+
+vcpkg_check_features("ssl" PAHO_WITH_SSL)
+
+# Link with 'paho-mqtt3as' library
+set(PAHO_C_LIBNAME paho-mqtt3as)
+
+# Setting the library path
+if (NOT DEFINED VCPKG_BUILD_TYPE OR VCPKG_BUILD_TYPE STREQUAL "release")
+  set(PAHO_C_LIBRARY_PATH "${CURRENT_INSTALLED_DIR}/lib")
+else()
+  set(PAHO_C_LIBRARY_PATH "${CURRENT_INSTALLED_DIR}/debug/lib")
+endif()
+
+# Setting the include path where MqttClient.h is present
+set(PAHO_C_INC "${CURRENT_INSTALLED_DIR}/include/paho-mqtt")
+
+# Set the generator to Ninja
+set(PAHO_CMAKE_GENERATOR "Ninja")
+
+# NOTE: the Paho C++ cmake files on Github are problematic. 
+# It uses two different options PAHO_BUILD_STATIC and PAHO_BUILD_SHARED instead of just using one variable.
+# Unless the open source community cleans up the cmake files, we are stuck with setting both of them.
+if (VCPKG_LIBRARY_LINKAGE STREQUAL "static")
+  set(PAHO_MQTTPP3_STATIC ON)
+  set(PAHO_MQTTPP3_SHARED OFF)
+  set(PAHO_C_LIB "${PAHO_C_LIBRARY_PATH}/${PAHO_C_LIBNAME}")
+  set(PAHO_OPTIONS -DPAHO_MQTT_C_LIBRARIES=${PAHO_C_LIB})
+else()
+  set(PAHO_MQTTPP3_STATIC OFF)
+  set(PAHO_MQTTPP3_SHARED ON)
+  set(PAHO_OPTIONS)
+endif()
+
+vcpkg_configure_cmake(
+  SOURCE_PATH ${SOURCE_PATH}
+  PREFER_NINJA
+  GENERATOR ${PAHO_CMAKE_GENERATOR}
+  OPTIONS
+  -DPAHO_BUILD_STATIC=${PAHO_MQTTPP3_STATIC}
+  -DPAHO_BUILD_SHARED=${PAHO_MQTTPP3_SHARED}
+  -DPAHO_WITH_SSL=${PAHO_WITH_SSL}
+  -DPAHO_MQTT_C_INCLUDE_DIRS=${PAHO_C_INC}
+  ${PAHO_OPTIONS}
+)
+
+# Run the build, copy pdbs and fixup the cmake targets
+vcpkg_install_cmake()
+vcpkg_copy_pdbs()
+vcpkg_fixup_cmake_targets(CONFIG_PATH "lib/cmake/PahoMqttCpp" TARGET_PATH "share/pahomqttcpp")
+
+# Remove the include and share folders in debug folder
+file(REMOVE_RECURSE ${CURRENT_PACKAGES_DIR}/debug/include)
+file(REMOVE_RECURSE ${CURRENT_PACKAGES_DIR}/debug/share)
+
+# Add copyright
+file(INSTALL ${SOURCE_PATH}/about.html DESTINATION ${CURRENT_PACKAGES_DIR}/share/paho-mqttpp3 RENAME copyright)