[libc][Obvious] Add "__" prefix to sched_getcpucount in the spec and elsewhere.

[sivachandra]

Summary

Without this fix, the declaration in sched.h will not have the "__" prefix and
will cause a compile failure.

libc/config/linux/x86_64/entrypoints.txt

list(APPEND TARGET_LIBC_ENTRYPOINTS
     libc.src.pthread.pthread_mutexattr_gettype
     libc.src.pthread.pthread_mutexattr_setpshared
     libc.src.pthread.pthread_mutexattr_setrobust
     libc.src.pthread.pthread_mutexattr_settype
     libc.src.pthread.pthread_once
     libc.src.pthread.pthread_setspecific
 
     # sched.h entrypoints
-    libc.src.sched.sched_getcpucount
+    libc.src.sched.__sched_getcpucount
 
     # stdio.h entrypoints
     libc.src.stdio.clearerr
     libc.src.stdio.clearerr_unlocked
     libc.src.stdio.fclose
     libc.src.stdio.flockfile
     libc.src.stdio.feof
     libc.src.stdio.feof_unlocked

libc/spec/llvm_libc_ext.td

def LLVMLibcExt : StandardSpec<"llvm_libc_ext"> {
   
   HeaderSpec Sched = HeaderSpec<
       "sched.h",
       [], // Macros
       [PidT, SizeTType, CpuSetT], // Types
       [], // Enumerations
       [
         FunctionSpec<
-            "sched_getcpucount",
+            "__sched_getcpucount",
             RetValSpec<IntType>,
             [ArgSpec<SizeTType>, ArgSpec<ConstCpuSetPtr>]
         >,
       ]
   >;
 
   let Headers = [
     String,
     Sched,
     Assert,
   ];
 }

libc/src/sched/CMakeLists.txt

 add_entrypoint_object(
   sched_setaffinity
   ALIAS
   DEPENDS
     .${LIBC_TARGET_OS}.sched_setaffinity
 )
 
 add_entrypoint_object(
-  sched_getcpucount
+  __sched_getcpucount
   ALIAS
   DEPENDS
-    .${LIBC_TARGET_OS}.sched_getcpucount
+    .${LIBC_TARGET_OS}.__sched_getcpucount
 )

libc/src/sched/linux/CMakeLists.txt

add_entrypoint_object(
   DEPENDS
     libc.include.errno
     libc.include.sched
     libc.src.__support.OSUtil.osutil
     libc.src.errno.errno
 )
 
 add_entrypoint_object(
-  sched_getcpucount
+  __sched_getcpucount
   SRCS
     sched_getcpucount.cpp
   HDRS
     ../sched_getcpucount.h
   DEPENDS
     libc.include.sched
 )

libc/test/src/sched/CMakeLists.txt

add_libc_unittest(
   SRCS
     cpu_count_test.cpp
   DEPENDS
     libc.include.errno
     libc.include.sched
     libc.include.sys_syscall
     libc.src.__support.OSUtil.osutil
     libc.src.sched.sched_getaffinity
-    libc.src.sched.sched_getcpucount
+    libc.src.sched.__sched_getcpucount
     libc.test.errno_setter_matcher
 )