From: Filip Kobierski <fkobi@pm.me>

This patches removes -O3 for g++ and unknown compilers.

Bug: https://bugs.gentoo.org/886443
--- a/configure.ac
+++ b/configure.ac
@@ -115,7 +115,7 @@
                 WSHADOW="-Wshadow"
                 ;;
         esac
-        CXXFLAGS="$CXXFLAGS -ftemplate-depth-40 -pedantic -O3 -Wall -W $WSHADOW -Wpointer-arith -Wcast-qual -Wwrite-strings -Wconversion -Wredundant-decls -Wno-long-long"
+        CXXFLAGS="$CXXFLAGS -ftemplate-depth-40 -pedantic -Wall -W $WSHADOW -Wpointer-arith -Wcast-qual -Wwrite-strings -Wconversion -Wredundant-decls -Wno-long-long"
         ;;
  icc | icpc)
         echo "Using INTEL icc"
@@ -125,7 +125,6 @@
         ;;
  *)
         echo "Using a unknown compiler"
-        CXXFLAGS="$CXXFLAGS -O3"
         ;;
 esac