brp-llvm-compile-lto-elf: Pass -r to xargs

If there are no .o/.a files to be distributed, this prevents
check_convert_bitcode from being called without a file argument,
in which case the first flag is going to be treated like the file
name, resulting in something like:

    realpath: invalid option -- 'O'
    Try 'realpath --help' for more information.
    Usage: file [-bcCdEhikLlNnprsSvzZ0] [--apple] [--extension] [--mime-encoding]
                [--mime-type] [-e <testname>] [-F <separator>]  [-f <namefile>]
                [-m <magicfiles>] [-P <parameter=value>] [--exclude-quiet]
                <file> ...
           file -C [-m <magicfiles>]
           file [--help]

brp-llvm-compile-lto-elf

@@ -43,4 +43,4 @@ check_convert_bitcode () {
 echo "Checking for LLVM bitcode artifacts"
 export -f check_convert_bitcode
 find "$RPM_BUILD_ROOT" -type f -name "*.[ao]" -print0 | \
-  xargs -0 -n1 -P$NCPUS sh -c "check_convert_bitcode \$@ $CLANG_FLAGS" ARG0
+  xargs -0 -r -n1 -P$NCPUS sh -c "check_convert_bitcode \$@ $CLANG_FLAGS" ARG0

redhat-rpm-config.spec

@@ -4,7 +4,7 @@
 # 2) When making changes, increment the version (in baserelease) by 1.
 #    rpmdev-bumpspec and other tools update the macro below, which is used
 #    in Version: to get the desired effect.
-%global baserelease 226
+%global baserelease 227
 
 Summary: Red Hat specific rpm configuration files
 Name: redhat-rpm-config
@@ -219,6 +219,9 @@ install -p -m 644 -t %{buildroot}%{_rpmluadir}/fedora/srpm forge.lua
 %doc buildflags.md
 
 %changelog
+* Fri Aug 05 2022 Nikita Popov <npopov@redhat.com> - 227-1
+- brp-llvm-compile-lto-elf: Pass -r to xargs
+
 * Wed Jun 22 2022 Timm Bäder <tbaeder@redhat.com> - 226-1
 - Move llvm_compile_lto_to_elf before __debug_install_post