Fix brp-llvm-compile-lto to not rely on a backtracking regex

Instead, grep the llvm-strings output for "-flto" and "-fno-lto" and
recognize the input as LTO input if -flto has a byte index greater than
-fno-lto.

brp-llvm-compile-lto-elf

@@ -16,14 +16,20 @@ check_convert_bitcode () {
   CLANG_FLAGS="$@"
 
   if [[ "${file_type}" == *"LLVM IR bitcode"* ]]; then
-    # check for an indication that the bitcode was
-    # compiled with -flto
-    llvm-bcanalyzer -dump ${file_name} | grep -xP '.*\-flto((?!-fno-lto).)*' 2>&1 > /dev/null
-    if [ $? -eq 0 ]; then
+    # Check the output of llvm-strings for the command line, which is in the LLVM bitcode because
+    # we pass -frecord-gcc-switches.
+    # Check for a line that has "-flto" after (or without) "-fno-lto".
+    llvm-strings ${file_name} | while read line ; do
+      flto=$(echo $line   | grep -o -b -e -flto     | tail -n 1 | cut -d : -f 1)
+      fnolto=$(echo $line | grep -o -b -e -fno-lto  | tail -n 1 | cut -d : -f 1)
+
+      if test -n "$flto" && { test -z "$fnolto" || test "$flto" -gt "$fnolto"; } ; then
         echo "Compiling LLVM bitcode file ${file_name}."
         clang ${CLANG_FLAGS} -fno-lto -Wno-unused-command-line-argument \
           -x ir ${file_name} -c -o ${file_name}
+        break
       fi
+      done
   elif [[ "${file_type}" == *"current ar archive"* ]]; then
     echo "Unpacking ar archive ${file_name} to check for LLVM bitcode components."
     # create archive stage for objects

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 231
+%global baserelease 232
 
 Summary: Red Hat specific rpm configuration files
 Name: redhat-rpm-config
@@ -221,6 +221,9 @@ install -p -m 644 -t %{buildroot}%{_rpmluadir}/fedora/srpm forge.lua
 %doc buildflags.md
 
 %changelog
+* Fri Sep 23 2022 Timm Bäder <tbaeder@redhat.com> - 232-1
+- Fix brp-compile-lto-elf to not rely on a backtracking regex
+
 * Thu Sep 08 2022 Maxwell G <gotmax@e.email> - 231-1
 - forge macros: Support Sourcehut. Fixes rhbz#2035935.