CI-unixish.yml: use LTO in the callgrind step

Author: firewave

.github/workflows/CI-unixish.yml

@@ -146,7 +146,8 @@ jobs:
         wget https://github.com/danmar/simplecpp/archive/refs/tags/1.5.1.tar.gz
         tar xvf 1.5.1.tar.gz
         make clean
-        make -j$(nproc) CXXOPTS="-O2 -g3"
+        # TODO: we could also use -O3 but that causes a performance regression with GCC
+        make -j$(nproc) CXXOPTS="-O2 -g3 -flto" LDOPTS="-flto"
         VALGRIND_TOOL=callgrind SIMPLECPP_PATH=simplecpp-1.5.1 ./selfcheck.sh >callgrind.log || (cat callgrind.log && false)
         cat callgrind.log
         for f in callgrind.out.*;