build system: only use -Wshadow-compatible-local if compiler supports it

Rakefile

@@ -139,7 +139,7 @@ def setup_globals
   cflags                   = "#{cflags_common} #{c(:USER_CFLAGS)}"
 
   cxxflags                 = "#{cflags_common} #{c(:STD_CXX)}"
-  cxxflags                += " -Wnon-virtual-dtor -Woverloaded-virtual -Wextra -Wno-missing-field-initializers -Wshadow-compatible-local #{c(:WNO_MAYBE_UNINITIALIZED)}"
+  cxxflags                += " -Wnon-virtual-dtor -Woverloaded-virtual -Wextra -Wno-missing-field-initializers #{c(:WSHADOW_COMPATIBLE_LOCAL)} #{c(:WNO_MAYBE_UNINITIALIZED)}"
   cxxflags                += " #{c(:QT_CFLAGS)} #{c(:BOOST_CPPFLAGS)} #{c(:USER_CXXFLAGS)}"
 
   ldflags                  = ""

ac/compiler_flags.m4

@@ -39,6 +39,21 @@ else
   fi
 fi
 
+AC_CACHE_CHECK([for compiler flag -Wshadow-compatible-local], [ax_cv_wshadow_compatible_local],[
+  AC_LANG_PUSH(C++)
+  CXXFLAGS_SAVED="$CXXFLAGS"
+  CXXFLAGS="$CXXFLAGS_SAVED -Wshadow-compatible-local"
+
+  AC_TRY_COMPILE([], [true;], [ax_cv_wshadow_compatible_local="yes"], [ax_cv_wshadow_compatible_local="no"])
+
+  AC_LANG_POP
+  CXXFLAGS="$CXXFLAGS_SAVED"
+])
+
+if test x"$ax_cv_wshadow_compatible_local" = xyes; then
+  WSHADOW_COMPATIBLE_LOCAL="-Wshadow-compatible-local"
+fi
+
 AC_SUBST(FSTACK_PROTECTOR)
 AC_SUBST(QUNUSED_ARGUMENTS)
 AC_SUBST(WNO_SELF_ASSIGN)
@@ -47,4 +62,5 @@ AC_SUBST(WLOGICAL_OP)
 AC_SUBST(WNO_INCONSISTENT_MISSING_OVERRIDE)
 AC_SUBST(WNO_POTENTIALLY_EVALUATED_EXPRESSION)
 AC_SUBST(WNO_MAYBE_UNINITIALIZED)
+AC_SUBST(WSHADOW_COMPATIBLE_LOCAL)
 AC_SUBST(LLVM_LLD)

build-config.in

@@ -136,6 +136,7 @@ WNO_MISMATCHED_TAGS = @WNO_MISMATCHED_TAGS@
 WNO_MAYBE_UNINITIALIZED = @WNO_MAYBE_UNINITIALIZED@
 WNO_POTENTIALLY_EVALUATED_EXPRESSION = @WNO_POTENTIALLY_EVALUATED_EXPRESSION@
 WNO_SELF_ASSIGN = @WNO_SELF_ASSIGN@
+WSHADOW_COMPATIBLE_LOCAL = @WSHADOW_COMPATIBLE_LOCAL@
 XSLTPROC = @XSLTPROC@
 XSLTPROC_FLAGS = @XSLTPROC_FLAGS@
 ZLIB_LIBS = @ZLIB_LIBS@