CONFIG/TEST: Fix compilation on gcc11

- Check if linker also supports -diag-error NNNN flag, since passing
  such flag to the gcc in compile mode just produces sime warnings but
  does not cause it to fail. On other hand, the GNU linker does fail
  when passed such (unsupported) flag.
- Make pgtable comparator a const function

config/m4/compiler.m4

@@ -205,7 +205,7 @@ AC_DEFUN([DETECT_UARCH],
 # CHECK_COMPILER_FLAG
 # Usage: CHECK_COMPILER_FLAG([name], [flag], [program], [if-true], [if-false])
 #
-# The macro checks if program may be compiled using specified flag
+# The macro checks if program may be compiled and linked using specified flag
 #
 AC_DEFUN([CHECK_COMPILER_FLAG],
 [
@@ -214,15 +214,15 @@ AC_DEFUN([CHECK_COMPILER_FLAG],
          SAVE_CXXFLAGS="$CFLAGS"
          CFLAGS="$BASE_CFLAGS $CFLAGS $2"
          CXXFLAGS="$BASE_CXXFLAGS $CXXFLAGS $2"
-         AC_COMPILE_IFELSE([$3],
-                           [AC_MSG_RESULT([yes])
-                            CFLAGS="$SAVE_CFLAGS"
-                            CXXFLAGS="$SAVE_CXXFLAGS"
-                            $4],
-                           [AC_MSG_RESULT([no])
-                            CFLAGS="$SAVE_CFLAGS"
-                            CXXFLAGS="$SAVE_CXXFLAGS"
-                            $5])
+         AC_LINK_IFELSE([$3],
+                        [AC_MSG_RESULT([yes])
+                         CFLAGS="$SAVE_CFLAGS"
+                         CXXFLAGS="$SAVE_CXXFLAGS"
+                         $4],
+                        [AC_MSG_RESULT([no])
+                         CFLAGS="$SAVE_CFLAGS"
+                         CXXFLAGS="$SAVE_CXXFLAGS"
+                         $5])
 ])
 
 

test/gtest/ucs/test_pgtable.cc

@@ -524,7 +524,9 @@ class test_pgtable_perf : public test_pgtable {
 
 private:
     struct region_comparator {
-        bool operator()(ucs_pgt_region_t* region1, ucs_pgt_region_t* region2) {
+        bool
+        operator()(ucs_pgt_region_t *region1, ucs_pgt_region_t *region2) const
+        {
             return region1->end <= region2->start;
         }
     };