build-sys: disable gc-sections if optimization is disabled

This way, development builds will not rely on gc-sections to
paper over cyclic link dependencies. Newly introduced broken
link requirements will immediatley fail.

Makefile.am

@@ -6549,9 +6549,7 @@ clean-local: $(CLEAN_LOCAL_HOOKS)
 	rm -f $(abs_srcdir)/hwdb/usb.ids $(abs_srcdir)/hwdb/pci.ids $(abs_srcdir)/hwdb/oui.txt \
 	      $(abs_srcdir)/hwdb/iab.txt
 
-# disable gc-sections to check limited toolchains for link breakage
 DISTCHECK_CONFIGURE_FLAGS = \
-	 CFLAGS='-fno-lto' LDFLAGS='-Wl,--as-needed -Wl,--no-gc-sections' \
 	--with-dbuspolicydir=$$dc_install_base/$(dbuspolicydir) \
 	--with-dbussessionservicedir=$$dc_install_base/$(dbussessionservicedir) \
 	--with-dbussystemservicedir=$$dc_install_base/$(dbussystemservicedir) \

configure.ac

@@ -183,8 +183,6 @@ CC_CHECK_FLAGS_APPEND([with_cflags], [CFLAGS], [\
         -fdiagnostics-show-option \
         -fno-strict-aliasing \
         -fvisibility=hidden \
-        -ffunction-sections \
-        -fdata-sections \
         -fstack-protector \
         -fstack-protector-strong \
         -fPIE \
@@ -208,10 +206,21 @@ AS_CASE([$CFLAGS], [*-O[[12345sz\ ]]*],
         [AC_MSG_RESULT([skipping -D_FORTIFY_SOURCE, optimization not enabled])])
 AC_SUBST([OUR_CPPFLAGS], "$with_cppflags $sanitizer_cppflags")
 
+AS_CASE([$CFLAGS], [*-O[[12345sz\ ]]*],
+        [CC_CHECK_FLAGS_APPEND([with_ldflags], [LDFLAGS], [\
+               -Wl,--gc-sections])],
+        [AC_MSG_RESULT([skipping --gc-sections, optimization not enabled])])
+AC_SUBST([OUR_CFLAGS], "$with_ldflags $sanitizer_cflags")
+
+AS_CASE([$CFLAGS], [*-O[[12345sz\ ]]*],
+        [CC_CHECK_FLAGS_APPEND([with_cflags], [CFLAGS], [\
+               -ffunction-sections -fdata-sections])],
+        [AC_MSG_RESULT([skipping -ffunction/data-section, optimization not enabled])])
+AC_SUBST([OUR_CFLAGS], "$with_cflags $sanitizer_cflags")
+
 CC_CHECK_FLAGS_APPEND([with_ldflags], [LDFLAGS], [\
         -Wl,--as-needed \
         -Wl,--no-undefined \
-        -Wl,--gc-sections \
         -Wl,-z,relro \
         -Wl,-z,now \
         -pie \