Stop using the __ANDROID_API_x__ constants.

Historically we've made a few mistakes where they haven't matched the
right number. And most non-Googlers are much more familiar with the
numbers, so it seems to make sense to rely more on them. Especially in
header files, which we actually expect real people to have to read from
time to time.

Test: treehugger
Change-Id: I0d4a97454ee108de1d32f21df285315c5488d886
diff --git a/libc/include/stdlib.h b/libc/include/stdlib.h
index b66e3c6..dc7b694 100644
--- a/libc/include/stdlib.h
+++ b/libc/include/stdlib.h
@@ -43,7 +43,7 @@
 
 __noreturn void abort(void);
 __noreturn void exit(int __status);
-#if __ANDROID_API__ >= __ANDROID_API_L__
+#if __ANDROID_API__ >= 21
 __noreturn void _Exit(int __status) __INTRODUCED_IN(21);
 #else
 __noreturn void _Exit(int) __RENAME(_exit);
@@ -167,7 +167,7 @@
 
 size_t wcstombs(char* __dst, const wchar_t* __src, size_t __n);
 
-#if __ANDROID_API__ >= __ANDROID_API_L__
+#if __ANDROID_API__ >= 21
 size_t __ctype_get_mb_cur_max(void) __INTRODUCED_IN(21);
 #define MB_CUR_MAX __ctype_get_mb_cur_max()
 #else
@@ -183,7 +183,7 @@
 #include <bits/fortify/stdlib.h>
 #endif
 
-#if __ANDROID_API__ >= __ANDROID_API_K__
+#if __ANDROID_API__ >= 19
 int abs(int __x) __attribute_const__ __INTRODUCED_IN(19);
 long labs(long __x) __attribute_const__ __INTRODUCED_IN(19);
 long long llabs(long long __x) __attribute_const__ __INTRODUCED_IN(19);
@@ -191,7 +191,7 @@
 // Implemented as static inlines before 19.
 #endif
 
-#if __ANDROID_API__ >= __ANDROID_API_L__
+#if __ANDROID_API__ >= 21
 float strtof(const char* __s, char** __end_ptr) __INTRODUCED_IN(21);
 double atof(const char* __s) __attribute_pure__ __INTRODUCED_IN(21);
 int rand(void) __INTRODUCED_IN(21);
@@ -207,7 +207,7 @@
 // Implemented as static inlines before 21.
 #endif
 
-#if __ANDROID_API__ >= __ANDROID_API_O__
+#if __ANDROID_API__ >= 26
 double strtod_l(const char* __s, char** __end_ptr, locale_t __l) __INTRODUCED_IN(26);
 float strtof_l(const char* __s, char** __end_ptr, locale_t __l) __INTRODUCED_IN(26);
 long strtol_l(const char* __s, char** __end_ptr, int, locale_t __l) __INTRODUCED_IN(26);