build: split warnings out of CXXFLAGS

CXXFLAGS should not be modified anyway. Also, this will enable us to
selectively disable warnings.

configure.ac

@@ -291,21 +291,21 @@ if test "x$enable_werror" = "xyes"; then
 fi
 
 if test "x$CXXFLAGS_overridden" = "xno"; then
-  AX_CHECK_COMPILE_FLAG([-Wall],[CXXFLAGS="$CXXFLAGS -Wall"],,[[$CXXFLAG_WERROR]])
-  AX_CHECK_COMPILE_FLAG([-Wextra],[CXXFLAGS="$CXXFLAGS -Wextra"],,[[$CXXFLAG_WERROR]])
-  AX_CHECK_COMPILE_FLAG([-Wformat],[CXXFLAGS="$CXXFLAGS -Wformat"],,[[$CXXFLAG_WERROR]])
-  AX_CHECK_COMPILE_FLAG([-Wvla],[CXXFLAGS="$CXXFLAGS -Wvla"],,[[$CXXFLAG_WERROR]])
-  AX_CHECK_COMPILE_FLAG([-Wformat-security],[CXXFLAGS="$CXXFLAGS -Wformat-security"],,[[$CXXFLAG_WERROR]])
-  AX_CHECK_COMPILE_FLAG([-Wthread-safety-analysis],[CXXFLAGS="$CXXFLAGS -Wthread-safety-analysis"],,[[$CXXFLAG_WERROR]])
+  AX_CHECK_COMPILE_FLAG([-Wall],[WARN_CXXFLAGS="$WARN_CXXFLAGS -Wall"],,[[$CXXFLAG_WERROR]])
+  AX_CHECK_COMPILE_FLAG([-Wextra],[WARN_CXXFLAGS="$WARN_CXXFLAGS -Wextra"],,[[$CXXFLAG_WERROR]])
+  AX_CHECK_COMPILE_FLAG([-Wformat],[WARN_CXXFLAGS="$WARN_CXXFLAGS -Wformat"],,[[$CXXFLAG_WERROR]])
+  AX_CHECK_COMPILE_FLAG([-Wvla],[WARN_CXXFLAGS="$WARN_CXXFLAGS -Wvla"],,[[$CXXFLAG_WERROR]])
+  AX_CHECK_COMPILE_FLAG([-Wformat-security],[WARN_CXXFLAGS="$WARN_CXXFLAGS -Wformat-security"],,[[$CXXFLAG_WERROR]])
+  AX_CHECK_COMPILE_FLAG([-Wthread-safety-analysis],[WARN_CXXFLAGS="$WARN_CXXFLAGS -Wthread-safety-analysis"],,[[$CXXFLAG_WERROR]])
 
   ## Some compilers (gcc) ignore unknown -Wno-* options, but warn about all
   ## unknown options if any other warning is produced. Test the -Wfoo case, and
   ## set the -Wno-foo case if it works.
-  AX_CHECK_COMPILE_FLAG([-Wunused-parameter],[CXXFLAGS="$CXXFLAGS -Wno-unused-parameter"],,[[$CXXFLAG_WERROR]])
-  AX_CHECK_COMPILE_FLAG([-Wself-assign],[CXXFLAGS="$CXXFLAGS -Wno-self-assign"],,[[$CXXFLAG_WERROR]])
-  AX_CHECK_COMPILE_FLAG([-Wunused-local-typedef],[CXXFLAGS="$CXXFLAGS -Wno-unused-local-typedef"],,[[$CXXFLAG_WERROR]])
-  AX_CHECK_COMPILE_FLAG([-Wdeprecated-register],[CXXFLAGS="$CXXFLAGS -Wno-deprecated-register"],,[[$CXXFLAG_WERROR]])
-  AX_CHECK_COMPILE_FLAG([-Wimplicit-fallthrough],[CXXFLAGS="$CXXFLAGS -Wno-implicit-fallthrough"],,[[$CXXFLAG_WERROR]])
+  AX_CHECK_COMPILE_FLAG([-Wunused-parameter],[NOWARN_CXXFLAGS="$NOWARN_CXXFLAGS -Wno-unused-parameter"],,[[$CXXFLAG_WERROR]])
+  AX_CHECK_COMPILE_FLAG([-Wself-assign],[NOWARN_CXXFLAGS="$NOWARN_CXXFLAGS -Wno-self-assign"],,[[$CXXFLAG_WERROR]])
+  AX_CHECK_COMPILE_FLAG([-Wunused-local-typedef],[NOWARN_CXXFLAGS="$NOWARN_CXXFLAGS -Wno-unused-local-typedef"],,[[$CXXFLAG_WERROR]])
+  AX_CHECK_COMPILE_FLAG([-Wdeprecated-register],[NOWARN_CXXFLAGS="$NOWARN_CXXFLAGS -Wno-deprecated-register"],,[[$CXXFLAG_WERROR]])
+  AX_CHECK_COMPILE_FLAG([-Wimplicit-fallthrough],[NOWARN_CXXFLAGS="$NOWARN_CXXFLAGS -Wno-implicit-fallthrough"],,[[$CXXFLAG_WERROR]])
 fi
 
 # Check for optional instruction set support. Enabling these does _not_ imply that all code will
@@ -1281,6 +1281,8 @@ AC_SUBST(BITCOIN_TX_NAME)
 
 AC_SUBST(RELDFLAGS)
 AC_SUBST(DEBUG_CPPFLAGS)
+AC_SUBST(WARN_CXXFLAGS)
+AC_SUBST(NOWARN_CXXFLAGS)
 AC_SUBST(DEBUG_CXXFLAGS)
 AC_SUBST(ERROR_CXXFLAGS)
 AC_SUBST(GPROF_CXXFLAGS)
@@ -1392,7 +1394,7 @@ echo "  CC            = $CC"
 echo "  CFLAGS        = $CFLAGS"
 echo "  CPPFLAGS      = $DEBUG_CPPFLAGS $HARDENED_CPPFLAGS $CPPFLAGS"
 echo "  CXX           = $CXX"
-echo "  CXXFLAGS      = $DEBUG_CXXFLAGS $HARDENED_CXXFLAGS $ERROR_CXXFLAGS $GPROF_CXXFLAGS $CXXFLAGS"
+echo "  CXXFLAGS      = $DEBUG_CXXFLAGS $HARDENED_CXXFLAGS $WARN_CXXFLAGS $NOWARN_CXXFLAGS $ERROR_CXXFLAGS $GPROF_CXXFLAGS $CXXFLAGS"
 echo "  LDFLAGS       = $PTHREAD_CFLAGS $HARDENED_LDFLAGS $GPROF_LDFLAGS $LDFLAGS"
 echo "  ARFLAGS       = $ARFLAGS"
 echo

src/Makefile.am

@@ -5,7 +5,7 @@
 DIST_SUBDIRS = secp256k1 univalue
 
 AM_LDFLAGS = $(PTHREAD_CFLAGS) $(LIBTOOL_LDFLAGS) $(HARDENED_LDFLAGS) $(GPROF_LDFLAGS) $(SANITIZER_LDFLAGS)
-AM_CXXFLAGS = $(DEBUG_CXXFLAGS) $(HARDENED_CXXFLAGS) $(ERROR_CXXFLAGS) $(GPROF_CXXFLAGS) $(SANITIZER_CXXFLAGS)
+AM_CXXFLAGS = $(DEBUG_CXXFLAGS) $(HARDENED_CXXFLAGS) $(WARN_CXXFLAGS) $(NOWARN_CXXFLAGS) $(ERROR_CXXFLAGS) $(GPROF_CXXFLAGS) $(SANITIZER_CXXFLAGS)
 AM_CPPFLAGS = $(DEBUG_CPPFLAGS) $(HARDENED_CPPFLAGS)
 AM_LIBTOOLFLAGS = --preserve-dup-deps
 EXTRA_LIBRARIES =