Merge #18535: build: remove -Qunused-arguments workaround for clang + ccache

a029805 build: remove -Qunused-arguments workaround for clang + ccache (fanquake)

Pull request description:

  This was added in 386efb7 to address spammy Clang warnings when building with ccache.

  The issue was addressed in [ccache 3.2](https://bugzilla.samba.org/show_bug.cgi?id=8118), and from a look at most major distros, it's only Debian Jessie that has a version of ccache older than that ([3.1](https://packages.debian.org/jessie/ccache)).

  Therefore I think it's acceptable to drop this workaround, and re-enable warnings for unused driver arguments (when compiling using Clang and ccache).

ACKs for top commit:
  hebasto:
    ACK a029805.
  vasild:
    utACK a029805

Tree-SHA512: f887b9bd12f9c1c8d209943b86e8dafe33cfd1572912f2cafabe08ffe403973e48f0f7289280a8c6db9263c57aad43fbd4bb72f42db762eb090f3b1ef0538f43

Author: fanquake

configure.ac

@@ -1468,9 +1468,6 @@ if test "x$use_ccache" != "xno"; then
   fi
   AC_MSG_RESULT($use_ccache)
 fi
-if test "x$use_ccache" = "xyes"; then
-    AX_CHECK_PREPROC_FLAG([-Qunused-arguments],[CPPFLAGS="-Qunused-arguments $CPPFLAGS"])
-fi
 
 dnl enable wallet
 AC_MSG_CHECKING([if wallet should be enabled])