[libc] printf test no longer work after recent changes

[SchrodingerZhu]

After recent changes, printf family test no long work in full build mode.
In debug build, the program hang forever at the following scene:

❯ gdb /home/schrodinger/development/llvm-project/build-2/libc/test/src/stdio/libc.test.src.stdio.fprintf_test.__unit__.__build
__
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Reading symbols from /home/schrodinger/development/llvm-project/build-2/libc/test/src/stdio/libc.test.src.stdio.fprintf_test.__unit__.__build__...
(gdb) r
Starting program: /home/schrodinger/development/llvm-project/build-2/libc/test/src/stdio/libc.test.src.stdio.fprintf_test.__unit__.__build__ 
Missing separate debuginfos, use: zypper install glibc-debuginfo-2.39-9.1.aarch64
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib64/libthread_db.so.1".
[==========] Running 1 test from 1 test suite.
[ RUN      ] LlvmLibcFPrintfTest.WriteToFile
[       OK ] LlvmLibcFPrintfTest.WriteToFile (177 us)
Ran 1 tests.  PASS: 1  FAIL: 0
^C
Program received signal SIGINT, Interrupt.
0x0000fffff7ac7f58 in __lll_lock_wait_private () from /lib64/libc.so.6
Missing separate debuginfos, use: zypper install libgcc_s1-debuginfo-14.1.1+git10335-1.1.aarch64 libstdc++6-debuginfo-14.1.1+git10335-1.1.aarch64
(gdb) bt
#0  0x0000fffff7ac7f58 in __lll_lock_wait_private () from /lib64/libc.so.6
#1  0x0000fffff7ab4e04 in fflush () from /lib64/libc.so.6
#2  0x0000fffff7d4745c in std::basic_ostream<char, std::char_traits<char> >::flush() () from /lib64/libstdc++.so.6
#3  0x0000fffff7cc4004 in std::ios_base::Init::~Init() () from /lib64/libstdc++.so.6
#4  0x0000fffff7a83e58 in __cxa_finalize () from /lib64/libc.so.6
#5  0x0000fffff7cad9a0 in ?? () from /lib64/libstdc++.so.6
Backtrace 

In release build, I sometime get

[3128/4107] Running unit test libc.test.src.stdio.fprintf_test.__unit__
FAILED: libc/test/src/stdio/CMakeFiles/libc.test.src.stdio.fprintf_test.__unit__ /home/schrodinger/development/llvm-project/build-2/libc/test/src/stdio/CMakeFiles/libc.test.src.stdio.fprintf_test.__unit__ 
cd /home/schrodinger/development/llvm-project/build-2/libc/test/src/stdio && /home/schrodinger/development/llvm-project/build-2/libc/test/src/stdio/libc.test.src.stdio.fprintf_test.__unit__.__build__
[==========] Running 1 test from 1 test suite.
[ RUN      ] LlvmLibcFPrintfTest.WriteToFile
[       OK ] LlvmLibcFPrintfTest.WriteToFile (76 us)
Ran 1 tests.  PASS: 1  FAIL: 0
Fatal error: glibc detected an invalid stdio handle