Add one line to your C/C++ source to make it executable.

executable.c

///$(which true);FLAGS="-g -Wall -Wextra --std=c17 -O1 -fsanitize=address,undefined";THIS_FILE="$(cd "$(dirname "$0")"; pwd -P)/$(basename "$0")";OUT_FILE="/tmp/build-cache/$THIS_FILE";mkdir -p "$(dirname "$OUT_FILE")";test "$THIS_FILE" -ot "$OUT_FILE" || $(which clang || which gcc) $FLAGS "$THIS_FILE" -o "$OUT_FILE" || exit $?;exec bash -c "exec -a \"$0\" \"$OUT_FILE\" $([ $# -eq 0 ] || printf ' "%s"' "$@")"
#include <stdio.h>

int main() {
  printf("Hello world!\n");
  return 0;
}

executable.cpp

///$(which true);FLAGS="-g -Wall -Wextra --std=c++23 -O1 -fsanitize=address,undefined";THIS_FILE="$(cd "$(dirname "$0")"; pwd -P)/$(basename "$0")";OUT_FILE="/tmp/build-cache/$THIS_FILE";mkdir -p "$(dirname "$OUT_FILE")";test "$THIS_FILE" -ot "$OUT_FILE" || $(which clang++ || which g++) $FLAGS "$THIS_FILE" -o "$OUT_FILE" || exit $?;exec bash -c "exec -a \"$0\" \"$OUT_FILE\" $([ $# -eq 0 ] || printf ' "%s"' "$@")"
#include <iostream>

int main() {
  std::cerr << "Hello, world!" << std::endl;
  return 0;
}

with-shebang.shc

#!/bin/bash
///$(which true);FLAGS="-g -Wall -Wextra --std=c17 -O1 -fsanitize=address,undefined";THIS_FILE="$(cd "$(dirname "$0")"; pwd -P)/$(basename "$0")";OUT_FILE="/tmp/build-cache/$THIS_FILE";mkdir -p "$(dirname "$OUT_FILE")";test "$THIS_FILE" -ot "$OUT_FILE" || tail -c +12 "$0" | $(which clang || which gcc) $FLAGS -xc - -o "$OUT_FILE" || exit $?;exec -a "$0" "$OUT_FILE" "$@"
#include <stdio.h>

int main() {
  printf("Hello world!\n");
  return 0;
}

with-shebang.shcpp

#!/bin/bash
///$(which true);FLAGS="-g -Wall -Wextra --std=c++23 -O1 -fsanitize=address,undefined";THIS_FILE="$(cd "$(dirname "$0")"; pwd -P)/$(basename "$0")";OUT_FILE="/tmp/build-cache/$THIS_FILE";mkdir -p "$(dirname "$OUT_FILE")";test "$THIS_FILE" -ot "$OUT_FILE" || tail -c +12 "$0" | $(which clang++ || which g++ || which cpp) $FLAGS -xc++ - -o "$OUT_FILE" || exit $?;exec -a "$0" "$OUT_FILE" "$@"
#include <iostream>

int main() {
  std::cerr << "Hello, world!" << std::endl;
  return 0;
}

Thanks, I've incorporated some of your suggestions!