[libc] Fix sched_get_priority_max() syscall invocation

[tzussman]

Summary

Previously used SYS_sched_get_priority_min. This also updates the tests
for SCHED_RR and SCHED_FIFO to check max_priority > min_priority, rather
than >= in order to catch future breakages.

[michaelrj]

LGTM, thank you for catching this.

[tzussman]

FYI, I don't have commit permissions for the repo

[michaelrj]

That's fine, I'll land this for you.

libc/src/sched/linux/sched_get_priority_max.cpp

 #include "src/__support/common.h"
 #include "src/errno/libc_errno.h"
 
 #include <sys/syscall.h> // For syscall numbers.
 
 namespace __llvm_libc {
 
 LLVM_LIBC_FUNCTION(int, sched_get_priority_max, (int policy)) {
-  long ret = __llvm_libc::syscall_impl(SYS_sched_get_priority_min, policy);
+  long ret = __llvm_libc::syscall_impl(SYS_sched_get_priority_max, policy);
   if (ret < 0) {
     libc_errno = -ret;
     return -1;
   }
   return ret;
 }
 
 } // namespace __llvm_libc

libc/test/src/sched/get_priority_test.cpp

// SCHED_BATCH, SCHED_ISO, SCHED_IDLE, SCHED_DEADLINE
     ASSERT_GE(max_priority, 0);
     ASSERT_EQ(libc_errno, 0);
     int min_priority = __llvm_libc::sched_get_priority_min(policy);
     ASSERT_GE(min_priority, 0);
     ASSERT_EQ(libc_errno, 0);
 
     ASSERT_LE(max_priority, 99);
     ASSERT_GE(min_priority, 0);
-    ASSERT_GE(max_priority, min_priority);
+    ASSERT_GT(max_priority, min_priority);
   }
 
   {
     int policy = SCHED_RR;
     int max_priority = __llvm_libc::sched_get_priority_max(policy);
     ASSERT_GE(max_priority, 0);
     ASSERT_EQ(libc_errno, 0);
     int min_priority = __llvm_libc::sched_get_priority_min(policy);
     ASSERT_GE(min_priority, 0);
     ASSERT_EQ(libc_errno, 0);
 
     ASSERT_LE(max_priority, 99);
     ASSERT_GE(min_priority, 0);
-    ASSERT_GE(max_priority, min_priority);
+    ASSERT_GT(max_priority, min_priority);
   }
 }