./configure --enable-debug is broken

[amitdo]

It produces -O0 -O2, which means the compiler will use -O2 instead of -O0.

[amitdo]

https://www.gnu.org/software/autoconf/manual/autoconf-2.66/html_node/C_002b_002b-Compiler.html

— Macro: AC_PROG_CXX ([compiler-search-list])
...
If output variable CXXFLAGS was not already set, set it to -g -O2 for the GNU C++ compiler (-O2 on systems where G++ does not accept -g), or -g for other compilers. If your package does not like this default, then it is acceptable to insert the line : ${CXXFLAGS=""}
after AC_INIT and before AC_PROG_CXX to select an empty default instead.

[amitdo]

Also, we might want to use -Og instead of -O0.

[amitdo]

https://gcc.gnu.org/onlinedocs/gcc/Optimize-Options.html#Optimize-Options

-Og is supported since GCC 4.8.

[amitdo]

Clang accepts the -Og flag since version 4.0, but treats it as -O1.
https://clang.llvm.org/docs/CommandGuide/clang.html