[libc][test] use`llvm-project/libc/test/UnitTest/ErrnoSetterMatcher.h` when applicable

[SchrodingerZhu]

#79573 introduces macros for errno handling.
For unit tests, this can be further improved by using ErrnoSetterMatcher(which can clear errno properly to avoid interference with other tests).

For example,

int max_priority = LIBC_NAMESPACE::sched_get_priority_max(policy);
ASSERT_EQ(max_priority, -1);
ASSERT_EQ(libc_errno, EINVAL);

can be refactored into

ASSERT_THAT(LIBC_NAMESPACE::sched_get_priority_max(policy), returns(EQ(-1)),with_errno(EQ(EINVAL)));

[llvmbot]

@llvm/issue-subscribers-libc

Author: Schrodinger ZHU Yifan (SchrodingerZhu)

https://github.com//pull/79573 introduces macros for `errno` handling. For unit tests, this can be further improved by using `ErrnoSetterMatcher`(which are clear errno properly to avoid interference with other tests).

For example,

int max_priority = LIBC_NAMESPACE::sched_get_priority_max(policy);
ASSERT_EQ(max_priority, -1);
ASSERT_EQ(libc_errno, EINVAL);

can be refactored into

ASSERT_THAT(LIBC_NAMESPACE::sched_get_priority_max(policy), returns(EQ(-1)),with_errno(EQ(EINVAL)));