Revert "[libc++] Mark __{emplace,push}_back_slow_path as noinline (#94379)"

This reverts commit 1bafd02.

This breaks the LLDB data formatters which means these failures show up
on every premerge run. Reverting for now until fixing the LLDB
formatters can be coordinated with a relanding.

Author: boomanaiden154

libcxx/include/__vector/vector.h

@@ -1161,24 +1161,6 @@ vector<_Tp, _Allocator>::__emplace_back_slow_path(_Args&&... __args) {
   return this->__end_;
 }
 
-// This makes the compiler inline `__else()` if `__cond` is known to be false. Currently LLVM doesn't do that without
-// the `__builtin_constant_p`, since it considers `__else` unlikely even through it's known to be run.
-// See https://llvm.org/PR154292
-template <class _If, class _Else>
-_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 void __if_likely_else(bool __cond, _If __if, _Else __else) {
-  if (__builtin_constant_p(__cond)) {
-    if (__cond)
-      __if();
-    else
-      __else();
-  } else {
-    if (__cond) [[__likely__]]
-      __if();
-    else
-      __else();
-  }
-}
-
 template <class _Tp, class _Allocator>
 template <class... _Args>
 _LIBCPP_CONSTEXPR_SINCE_CXX20 inline
@@ -1189,14 +1171,12 @@ _LIBCPP_CONSTEXPR_SINCE_CXX20 inline
 #endif
     vector<_Tp, _Allocator>::emplace_back(_Args&&... __args) {
   pointer __end = this->__end_;
-  std::__if_likely_else(
-      __end < this->__cap_,
-      [&] {
-        __emplace_back_assume_capacity(std::forward<_Args>(__args)...);
-        ++__end;
-      },
-      [&] { __end = __emplace_back_slow_path(std::forward<_Args>(__args)...); });
-
+  if (__end < this->__cap_) {
+    __emplace_back_assume_capacity(std::forward<_Args>(__args)...);
+    ++__end;
+  } else {
+    __end = __emplace_back_slow_path(std::forward<_Args>(__args)...);
+  }
   this->__end_ = __end;
 #if _LIBCPP_STD_VER >= 17
   return *(__end - 1);