[libc][math] Refactor ldexpf implementation to header-only in src/__support/math folder (#147906)

Part of #147386

in preparation for:
https://discourse.llvm.org/t/rfc-make-clang-builtin-math-functions-constexpr-with-llvm-libc-to-support-c-23-constexpr-math-functions/86450

Please merge #147901 first

@lntue

libc/shared/math.h

@@ -16,6 +16,7 @@
 #include "math/frexpf.h"
 #include "math/frexpf128.h"
 #include "math/frexpf16.h"
+#include "math/ldexpf.h"
 #include "math/ldexpf128.h"
 #include "math/ldexpf16.h"
 

libc/shared/math/ldexpf.h

@@ -0,0 +1,23 @@
+//===-- Shared ldexpf function ----------------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SHARED_MATH_LDEXPF_H
+#define LLVM_LIBC_SHARED_MATH_LDEXPF_H
+
+#include "shared/libc_common.h"
+#include "src/__support/math/ldexpf.h"
+
+namespace LIBC_NAMESPACE_DECL {
+namespace shared {
+
+using math::ldexpf;
+
+} // namespace shared
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SHARED_MATH_LDEXPF_H