Don't deoptimize llvm when --enable-debug

libLTO fails to link here.

Author: brson

configure

@@ -631,7 +631,6 @@ if [ -n "$CFG_ENABLE_DEBUG" ]; then
     msg "debug mode enabled, setting performance options"
     CFG_DISABLE_OPTIMIZE=1
     CFG_DISABLE_OPTIMIZE_CXX=1
-    CFG_DISABLE_OPTIMIZE_LLVM=1
     CFG_ENABLE_LLVM_ASSERTIONS=1
     CFG_ENABLE_DEBUG_ASSERTIONS=1
     CFG_ENABLE_DEBUG_JEMALLOC=1