c-api: Bring wasmtime-cpp into this repository.

`wasmtime-cpp/include/wasmtime.hh` -> `/crates/c-api/include/`
`wasmtime-cpp/tests/*` -> `/crates/c-api/tests/`
`wasmtime-cpp/examples/*` -> `/examples/`

See discussion in bytecodealliance#10566 for more context.

Author: MangoPeachGrape

crates/c-api/CMakeLists.txt

@@ -1,8 +1,9 @@
 cmake_minimum_required(VERSION 3.12)
-project(wasmtime C)
+project(wasmtime)
 
 set(WASMTIME_USER_CARGO_BUILD_OPTIONS "" CACHE STRING "Additional cargo flags (such as --features) to apply to the build command")
 option(BUILD_SHARED_LIBS "Build using shared libraries" OFF)
+option(BUILD_TESTS "Build tests" ON)
 option(WASMTIME_ALWAYS_BUILD "If cmake should always invoke cargo to build wasmtime" ON)
 option(WASMTIME_FASTEST_RUNTIME "Set flags designed to optimize runtime performance" OFF)
 set(WASMTIME_TARGET "" CACHE STRING "Rust target to build for")
@@ -129,3 +130,43 @@ add_custom_target(headers-to-doc
       -DWASMTIME_HEADER_DST=${CMAKE_BINARY_DIR}/include
       -P ${CMAKE_CURRENT_SOURCE_DIR}/cmake/install-headers.cmake
   DEPENDS ${headers})
+
+if (NOT CMAKE_CXX_STANDARD)
+  message(STATUS "Cannot detect C++ Standard. Switching to C++17 by default !!")
+  set(CMAKE_CXX_STANDARD 17)
+endif()
+message(STATUS "CMAKE_CXX_STANDARD is ${CMAKE_CXX_STANDARD}")
+if (NOT CMAKE_CXX_STANDARD GREATER_EQUAL 17)
+  message(FATAL_ERROR "WASMTIME_CPP library does not support ${CMAKE_CXX_STANDARD}")
+endif()
+set(CMAKE_CXX_STANDARD_REQUIRED True)
+
+option(ENABLE_CODE_ANALYSIS "Run code analysis" OFF)
+message(STATUS "ENABLE_CODE_ANALYSIS       ${ENABLE_CODE_ANALYSIS}")
+
+if ("${CMAKE_CXX_COMPILER_ID}" STREQUAL "GNU")
+   add_compile_options (-fdiagnostics-color=always)
+elseif ("${CMAKE_CXX_COMPILER_ID}" STREQUAL "Clang")
+   add_compile_options (-fcolor-diagnostics)
+endif ()
+
+add_library(wasmtime-cpp INTERFACE)
+target_link_libraries(wasmtime-cpp INTERFACE wasmtime)
+if (MSVC)
+  target_compile_options(wasmtime-cpp INTERFACE /DWASM_API_EXTERN= /DWASI_API_EXTERN=)
+  target_link_libraries(wasmtime-cpp INTERFACE ws2_32 bcrypt advapi32 userenv ntdll shell32 ole32)
+else()
+  target_link_libraries(wasmtime-cpp INTERFACE stdc++ pthread)
+endif()
+
+target_include_directories(
+        wasmtime-cpp
+        INTERFACE
+        ${PROJECT_SOURCE_DIR}/include)
+
+if (BUILD_TESTS)
+  message(STATUS "Building tests")
+  set(INSTALL_GTEST OFF CACHE BOOL "" FORCE)
+  enable_testing()
+  add_subdirectory(tests)
+endif()