build-sys: Sync CFLAGS with libostree

In particular this pulls in `-fno-strict-aliasing`.  See
https://github.com/ostreedev/ostree/pull/1384

Closes: #1156
Approved by: jlebon

Makefile.am

@@ -39,7 +39,9 @@ AM_CPPFLAGS += -DDATADIR='"$(datadir)"' \
         -DRPM_OSTREE_FEATURES='"$(RPM_OSTREE_FEATURES)"' \
 	-DRPM_OSTREE_GITREV='"$(RPM_OSTREE_GITREV)"' \
 	-DGLIB_VERSION_MIN_REQUIRED=GLIB_VERSION_2_50 -DGLIB_VERSION_MAX_ALLOWED=GLIB_VERSION_2_50
-AM_CFLAGS += -std=gnu11 $(WARN_CFLAGS)
+# Keep this in sync with the AM_CFLAGS in libostree; see
+# that project for more information about e.g. -fno-strict-aliasing
+AM_CFLAGS += -std=gnu11 -fno-strict-aliasing $(WARN_CFLAGS)
 # bundled libdnf
 AM_LDFLAGS += "-Wl,-rpath=$(libdir)/rpm-ostree"
 

configure.ac

@@ -38,24 +38,29 @@ AC_SUBST([dbusservicedir], [$dbusservicedir])
 AC_MSG_RESULT(dbusservicedir)
 
 dnl Keep this in sync with the version in ostree
+AS_IF([echo "$CFLAGS" | grep -q -E -e '-Werror($| )'], [], [
 CC_CHECK_FLAGS_APPEND([WARN_CFLAGS], [CFLAGS], [\
-        -pipe \
-        -Wall \
-	-Werror=empty-body \
-	-Werror=strict-prototypes \
-	-Werror=missing-prototypes \
-	-Werror=implicit-function-declaration \
-        "-Werror=format=2 -Werror=format-security -Werror=format-nonliteral" \
-	-Werror=pointer-arith -Werror=init-self \
-        -Werror=missing-declarations \
-        -Werror=return-type \
-        -Werror=overflow \
-        -Werror=int-conversion \
-        -Werror=parenthesis \
-        -Werror=incompatible-pointer-types \
-        -Werror=misleading-indentation \
-	-Werror=missing-include-dirs -Werror=aggregate-return \
-])
+  -pipe \
+  -Wall \
+  -Werror=empty-body \
+  -Werror=strict-prototypes \
+  -Werror=missing-prototypes \
+  -Werror=implicit-function-declaration \
+  "-Werror=format=2 -Werror=format-security -Werror=format-nonliteral" \
+  -Werror=pointer-arith -Werror=init-self \
+  -Werror=missing-declarations \
+  -Werror=return-type \
+  -Werror=switch \
+  -Werror=overflow \
+  -Werror=int-conversion \
+  -Werror=parenthesis \
+  -Werror=undef \
+  -Werror=incompatible-pointer-types \
+  -Werror=misleading-indentation \
+  -Werror=missing-include-dirs -Werror=aggregate-return \
+  -Wstrict-aliasing=2 \
+  -Werror=unused-result \
+])])
 AC_SUBST(WARN_CFLAGS)
 
 AC_MSG_CHECKING([for -fsanitize=address in CFLAGS])