first commit

nghttp2/cmake/ExtractValidFlags.cmake

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+# Convenience function that checks the availability of certain
+# C or C++ compiler flags and returns valid ones as a string.
+
+include(CheckCCompilerFlag)
+include(CheckCXXCompilerFlag)
+
+function(extract_valid_c_flags varname)
+  set(valid_flags)
+  foreach(flag IN LISTS ARGN)
+    string(REGEX REPLACE "[^a-zA-Z0-9_]+" "_" flag_var ${flag})
+    set(flag_var "C_FLAG_${flag_var}")
+    check_c_compiler_flag("${flag}" "${flag_var}")
+    if(${flag_var})
+      set(valid_flags "${valid_flags} ${flag}")
+    endif()
+  endforeach()
+  set(${varname} "${valid_flags}" PARENT_SCOPE)
+endfunction()
+
+function(extract_valid_cxx_flags varname)
+  set(valid_flags)
+  foreach(flag IN LISTS ARGN)
+    string(REGEX REPLACE "[^a-zA-Z0-9_]+" "_" flag_var ${flag})
+    set(flag_var "CXX_FLAG_${flag_var}")
+    check_cxx_compiler_flag("${flag}" "${flag_var}")
+    if(${flag_var})
+      set(valid_flags "${valid_flags} ${flag}")
+    endif()
+  endforeach()
+  set(${varname} "${valid_flags}" PARENT_SCOPE)
+endfunction()