rules.mak: Also try -r to build modules

Building qemu fails in distributions where gcc enables PIE by default
(e.g. Debian unstable) with:

/usr/bin/ld: -r and -pie may not be used together

You have to use -r instead of -Wl,-r to avoid gcc passing -pie to the linker
when PIE is enabled and a relocatable object is passed.  However, clang
does not know about -r, so try -Wl,-r first.

[This is a fix for commit c96f0ee6a6
("rules.mak: Use -r instead of -Wl, -r to fix building when PIE is
default") which mostly worked but broke the ./configure --enable-modules
build with clang.
--Stefan]

Reported-by: Adrian Bunk <bunk@stusta.de>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-id: 20161129153720.29747-1-pbonzini@redhat.com
Cc: qemu-stable@nongnu.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

configure

@@ -4723,8 +4723,14 @@ EOF
 if ! compile_object ""; then
   error_exit "Failed to compile object file for LD_REL_FLAGS test"
 fi
-if do_cc -nostdlib -Wl,-r -Wl,--no-relax -o $TMPMO $TMPO; then
+for i in '-Wl,-r -Wl,--no-relax' -Wl,-r -r; do
-  LD_REL_FLAGS="-Wl,--no-relax"
+  if do_cc -nostdlib $i -o $TMPMO $TMPO; then
+    LD_REL_FLAGS=$i
+    break
+  fi
+done
+if test "$modules" = "yes" && test "$LD_REL_FLAGS" = ""; then
+  feature_not_found "modules" "Cannot find how to build relocatable objects"
 fi
 
 ##########################################

rules.mak

@@ -93,7 +93,7 @@ module-common.o: CFLAGS += $(DSO_OBJ_CFLAGS)
 	$(if $(findstring /,$@),$(call quiet-command,cp $@ $(subst /,-,$@),"CP","$(subst /,-,$@)"))
 
 
-LD_REL := $(CC) -nostdlib -r $(LD_REL_FLAGS)
+LD_REL := $(CC) -nostdlib $(LD_REL_FLAGS)
 
 %.mo:
 	$(call quiet-command,$(LD_REL) -o $@ $^,"LD","$(TARGET_DIR)$@")