CMake: Fix accidental variable expansion of WASI (#45)

Author: kateinoigakukun

CMakeLists.txt

@@ -57,7 +57,7 @@ if(CMAKE_SYSTEM_NAME STREQUAL Windows)
         $<$<COMPILE_LANGUAGE:C,CXX>:U_TIMEZONE=_timezone>
         $<$<COMPILE_LANGUAGE:C,CXX>:_CRT_SECURE_NO_DEPRECATE>
         $<$<COMPILE_LANGUAGE:C,CXX>:U_PLATFORM_USES_ONLY_WIN32_API>)
-elseif(CMAKE_SYSTEM_NAME STREQUAL WASI)
+elseif(CMAKE_SYSTEM_NAME STREQUAL "WASI")
     # WASI specific settings
     add_compile_definitions(
         $<$<COMPILE_LANGUAGE:C,CXX>:U_HAVE_TZSET=0>