Add native and cross compiling CMake build support

cmake/modules/IntrospectSystem.cmake

@@ -0,0 +1,52 @@
+# system capabilities checking
+
+# initial system defaults
+if(CMAKE_COMPILER_IS_GNUCC)
+  set(MRUBY_DEFAULT_CFLAGS "-Wall -Werror-implicit-function-declaration")
+  set(CMAKE_C_FLAGS "${MRUBY_DEFAULT_CFLAGS}")
+  set(CMAKE_C_FLAGS_DEBUG "-O3 -ggdb")
+  set(CMAKE_C_FLAGS_MINSIZEREL "-Os -DNDEBUG")
+  set(CMAKE_C_FLAGS_RELWITHDEBINFO "-O3 -g")
+  set(CMAKE_C_FLAGS_RELEASE "-O3 -DNDEBUG")
+
+  set(MRUBY_LIBS m)
+else()
+  if(MSVC)
+    # TODO default MSVC flags
+    add_definitions(
+      -D_CRT_SECURE_NO_WARNINGS
+      -wd4018  # suppress 'signed/unsigned mismatch'
+      )
+  endif()
+endif()
+
+if(MSVC)
+  add_definitions(
+    -DRUBY_EXPORT   # required by oniguruma.h
+    )
+endif()
+
+
+# include helpers
+include(CheckIncludeFile)
+include(CheckSymbolExists)
+
+# header checks
+CHECK_INCLUDE_FILE(string.h HAVE_STRING_H)
+if(HAVE_STRING_H)
+  add_definitions(-DHAVE_STRING_H)
+endif()
+
+CHECK_INCLUDE_FILE(float.h HAVE_FLOAT_H)
+if(HAVE_FLOAT_H)
+  add_definitions(-DHAVE_FLOAT_H)
+endif()
+
+
+# symbol checks
+CHECK_SYMBOL_EXISTS(gettimeofday sys/time.h HAVE_GETTIMEOFDAY)
+if(NOT HAVE_GETTIMEOFDAY)
+  add_definitions(-DNO_GETTIMEOFDAY)
+endif()
+
+# vim: ts=2 sts=2 sw=2 et