Clean up some code

- Use good ELF technique in cosmo_dlopen()
- Make strerror() conform more to other libc impls
- Introduce __clear_cache() and use it in cosmo_dlopen()
- Remove libc/fmt/fmt.h header (trying to kill off LIBC_FMT)

libc/runtime/printgarbage.c

@@ -16,7 +16,6 @@
 │ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
 │ PERFORMANCE OF THIS SOFTWARE.                                                │
 ╚─────────────────────────────────────────────────────────────────────────────*/
-#include "libc/fmt/fmt.h"
 #include "libc/intrin/kprintf.h"
 #include "libc/log/log.h"
 #include "libc/nexgen32e/gc.internal.h"

libc/runtime/runtime.h

@@ -115,6 +115,7 @@ bool32 _isheap(void *);
 /* code morphing */
 void __morph_begin(void);
 void __morph_end(void);
+void __clear_cache(void *, void *);
 /* portability */
 int NtGetVersion(void) pureconst;
 bool32 IsGenuineBlink(void);