Add cpu / mem / fsz limits to build system

Thanks to all the refactorings we now have the ability to enforce
reasonable limitations on the amount of resources any individual
compile or test can consume. Those limits are currently:

- `-C 8` seconds of 3.1ghz CPU time
- `-M 256mebibytes` of virtual memory
- `-F 100megabyte` limit on file size

Only one file currently needs to exceed these limits:

    o/$(MODE)/third_party/python/Objects/unicodeobject.o: \
        QUOTA += -C16  # overrides cpu limit to 16 seconds

This change introduces a new sizetol() function to LIBC_FMT for parsing
byte or bit size strings with Si unit suffixes. Functions like atoi()
have been rewritten too.

libc/fmt/strtoull.c

@@ -17,19 +17,22 @@
 │ PERFORMANCE OF THIS SOFTWARE.                                                │
 ╚─────────────────────────────────────────────────────────────────────────────*/
 #include "libc/fmt/conv.h"
-#include "libc/errno.h"
 #include "libc/limits.h"
 
-unsigned long long strtoull(const char *s, char **endptr, int optional_base) {
-  intmax_t res;
-  res = strtoimax(s, endptr, optional_base);
-  if (res < ULONG_LONG_MIN) {
-    errno = ERANGE;
-    return ULONG_LONG_MIN;
-  }
-  if (res > ULONG_LONG_MAX) {
-    errno = ERANGE;
-    return ULONG_LONG_MAX;
-  }
-  return res;
+/**
+ * Decodes unsigned integer from ASCII string.
+ *
+ * @param s is a non-null nul-terminated string
+ * @param endptr if non-null will always receive a pointer to the char
+ *     following the last one this function processed, which is usually
+ *     the NUL byte, or in the case of invalid strings, would point to
+ *     the first invalid character
+ * @param base can be anywhere between [2,36] or 0 to auto-detect based
+ *     on the the prefixes 0 (octal), 0x (hexadecimal), 0b (binary), or
+ *     decimal (base 10) by default
+ * @return decoded integer mod 2⁶⁴ negated if leading `-`
+ */
+unsigned long long strtoull(const char *s, char **endptr, int base) {
+  _Static_assert(LONG_MAX == LONG_LONG_MAX, "need strtoull impl");
+  return strtoul(s, endptr, base);
 }