aslp-cpp: roll httplib to fix user-defined string warning

[katrinafyi]

new clang warning: https://github.com/yhirose/cpp-httplib/pull/1962

[78/89] Building CXX object
_deps/aslp-cpp-build/CMakeFiles/aslp-cpp_aslp-cpp.dir/source/aslp-cpp.cpp.o
In file included from
/home/regehr/alive2-regehr/build/_deps/aslp-cpp-src/aslp-cpp/source/aslp-cpp.cpp:22:
/home/regehr/alive2-regehr/build/_deps/aslp-cpp-src/aslp-cpp/lib/httplib.h:3432:42:
warning: identifier '_t' preceded by whitespace in a literal operator
declaration is deprecated [-Wdeprecated-literal-operator]
  3432 | inline constexpr unsigned int operator"" _t(const char *s,
size_t l) {
       |                               ~~~~~~~~~~~^~
       |                               operator""_t
1 warning generated.