[gn build] Set HAVE_MALLINFO2=1

I'm seeing deprecated warnings due to using mallinfo() instead of
mallinfo2().

  ../../llvm/lib/Support/Unix/Process.inc:98:10: warning: 'mallinfo' is deprecated [-Wdeprecated-declarations]
    mi = ::mallinfo();

mallinfo2() is part of glibc 2.33 which was released in Feb 2021, which
is fairly recent but I think gn users should be using fairly up to date
glibcs.

If this breaks people we could make this a gn arg instead.

Differential Revision: https://reviews.llvm.org/D117916

llvm/utils/gn/secondary/llvm/include/llvm/Config/BUILD.gn

@@ -89,7 +89,6 @@ write_cmake_config("config") {
     "HAVE_LIBPFM=",
     "HAVE_LIBPSAPI=",
     "HAVE_MALLCTL=",
-    "HAVE_MALLINFO2=",
     "HAVE_SIGNAL_H=1",
     "HAVE_STD_IS_TRIVIALLY_COPYABLE=1",
     "HAVE_STRERROR=1",
@@ -143,6 +142,7 @@ write_cmake_config("config") {
       "HAVE_LINK_H=1",
       "HAVE_LSEEK64=1",
       "HAVE_MALLINFO=1",
+      "HAVE_MALLINFO2=1",
       "HAVE_STRUCT_STAT_ST_MTIM_TV_NSEC=1",
     ]
   } else {
@@ -151,6 +151,7 @@ write_cmake_config("config") {
       "HAVE_LINK_H=",
       "HAVE_LSEEK64=",
       "HAVE_MALLINFO=",
+      "HAVE_MALLINFO2=",
       "HAVE_STRUCT_STAT_ST_MTIM_TV_NSEC=",
     ]
   }