diff -up ./compiler_opt.py.bak ./compiler_opt.py
--- ./compiler_opt.py.bak	2019-01-19 22:52:55.000000000 +0100
+++ ./compiler_opt.py	2019-02-15 16:40:42.739281229 +0100
@@ -334,7 +334,6 @@ def set_compiler_options(package_root, e
 
     # Options specific to GCC and CLANG
     if clang or gcc:
-        extra_cc_options.append('-O3')
         if compiler_supports_sse2_with_x86intrin_h():
             extra_cc_options.append('-msse2')
             extra_macros.append(("HAVE_X86INTRIN_H", None))