[libc] fix up fileno tests (#85660)

Fixes #85628

Author: nickdesaulniers

libc/config/gpu/entrypoints.txt

@@ -179,6 +179,7 @@ set(TARGET_LIBC_ENTRYPOINTS
     libc.src.stdio.ferror
     libc.src.stdio.fseek
     libc.src.stdio.fflush
+    libc.src.stdio.fileno
     libc.src.stdio.ftell
     libc.src.stdio.clearerr
     libc.src.stdio.puts

libc/config/linux/aarch64/entrypoints.txt

@@ -542,6 +542,7 @@ if(LLVM_LIBC_FULL_BUILD)
     libc.src.stdio.ferror_unlocked
     libc.src.stdio.fgetc
     libc.src.stdio.fflush
+    libc.src.stdio.fileno
     libc.src.stdio.fopen
     libc.src.stdio.fputc
     libc.src.stdio.fputs

libc/config/linux/riscv/entrypoints.txt

@@ -565,6 +565,7 @@ if(LLVM_LIBC_FULL_BUILD)
     libc.src.stdio.fgetc_unlocked
     libc.src.stdio.fgets
     libc.src.stdio.fflush
+    libc.src.stdio.fileno
     libc.src.stdio.fopen
     libc.src.stdio.fputc
     libc.src.stdio.fputs

libc/test/src/stdio/CMakeLists.txt

@@ -14,6 +14,7 @@ add_libc_test(
     libc.src.stdio.feof
     libc.src.stdio.ferror
     libc.src.stdio.fflush
+    libc.src.stdio.fileno
     libc.src.stdio.fopen
     libc.src.stdio.fputs
     libc.src.stdio.fread

libc/test/src/stdio/fileop_test.cpp

@@ -11,6 +11,7 @@
 #include "src/stdio/feof.h"
 #include "src/stdio/ferror.h"
 #include "src/stdio/fflush.h"
+#include "src/stdio/fileno.h"
 #include "src/stdio/fopen.h"
 #include "src/stdio/fputs.h"
 #include "src/stdio/fread.h"