compile_flag: add multiple flag search

compile_flag.cmake

@@ -9,6 +9,11 @@ include(CMakeCheckCompilerFlagCommonPatterns)
 # -fsanitize=address is impossible with this macro.
 #
 # Instead, we roll out own. Yay cmake...
+#
+# Accepts a second parameter that names an output variable. It will be set to
+# 1 if-and-only-if the flag was accepted by the compiler. Otherwise it will be
+# left untouched. It is up to the user to reset this flag between invocations
+# if necessary.
 macro (append_compile_flag _flag)
     string (MAKE_C_IDENTIFIER ${_flag} _name)
 
@@ -48,5 +53,32 @@ macro (append_compile_flag _flag)
 
     if (compile_flag_${_name})
         set (CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${_flag}")
+        if (${ARGC} GREATER_EQUAL 2)
+            set(${ARGV1} 1)
+        endif()
     endif()
 endmacro(append_compile_flag)
+
+
+# Find the first compile flag in the list of arguments that is supported by
+# the compiler and set it.
+macro (append_first_compile_flag)
+    message(CHECK_START "First CXXFLAGS ${ARGV}")
+    foreach(__append_first_compile_flag__flag ${ARGV})
+        set(__append_first_compile_flag__test 0)
+
+        append_compile_flag(
+            ${__append_first_compile_flag__flag}
+            __append_first_compile_flag__test
+        )
+
+        if (${__append_first_compile_flag__test})
+            message(CHECK_PASS "Found ${__append_first_compile_flag__flag}")
+            break()
+        endif()
+    endforeach()
+
+    if (NOT ${__append_first_compile_flag__test})
+        message(CHECK_FAIL "No valid flags")
+    endif ()
+endmacro()