LibC: Drop complex.cpp and move its definitions to complex.h

libc++ disallows including LibC's complex.h in C++ mode. This means that
a C++ file cannot expect LibC's complex.h to be included, and thus
cannot use c-prefixed complex number functions. As a result,
complex.cpp is broken when libc++ has a higher include priority
than LibC.

A check for __cplusplus has been added to complex.h to warn users of
toolchains that don't use libc++.

Userland/Libraries/LibC/CMakeLists.txt

@@ -1,7 +1,6 @@
 set(LIBC_SOURCES
     arpa/inet.cpp
     assert.cpp
-    complex.cpp
     ctype.cpp
     cxxabi.cpp
     dirent.cpp

Userland/Libraries/LibC/complex.cpp

@@ -1,46 +0,0 @@
-/*
- * Copyright (c) 2022, Peter Elliott <pelliott@serenityos.org>
- *
- * SPDX-License-Identifier: BSD-2-Clause
- */
-
-#include <complex.h>
-
-extern "C" {
-
-// Function definitions of this form "type (name)(args)" are intentional, to
-// prevent macro versions of "name" from being incorrectly expanded. These
-// functions are here to provide external linkage to their macro implementations.
-
-// https://pubs.opengroup.org/onlinepubs/9699919799/functions/creal.html
-float(crealf)(float complex z)
-{
-    return crealf(z);
-}
-
-double(creal)(double complex z)
-{
-    return creal(z);
-}
-
-long double(creall)(long double complex z)
-{
-    return creall(z);
-}
-
-// https://pubs.opengroup.org/onlinepubs/9699919799/functions/cimag.html
-double(cimag)(double complex z)
-{
-    return cimag(z);
-}
-
-float(cimagf)(float complex z)
-{
-    return cimagf(z);
-}
-
-long double(cimagl)(long double complex z)
-{
-    return cimagl(z);
-}
-}

Userland/Libraries/LibC/complex.h

@@ -11,6 +11,10 @@
 
 #pragma once
 
+#ifdef __cplusplus
+#    error "C++ code must not include complex.h. Use AK/Complex.h instead."
+#endif
+
 #include <stddef.h>
 #include <sys/cdefs.h>
 
@@ -25,14 +29,6 @@ __BEGIN_DECLS
 #define CMPLXF(x, y) ((float complex)__builtin_complex((float)x, (float)y))
 #define CMPLXL(x, y) ((long double complex)__builtin_complex((long double)x, (long double)y))
 
-float crealf(float complex z);
-double creal(double complex z);
-long double creall(long double complex z);
-
-double cimag(double complex z);
-float cimagf(float complex z);
-long double cimagl(long double complex z);
-
 // These are macro implementations of the above functions, so that they will always be inlined.
 #define creal(z) ((double)__real__((double complex)z))
 #define crealf(z) ((float)__real__((float complex)z))
@@ -42,4 +38,40 @@ long double cimagl(long double complex z);
 #define cimagf(z) ((float)__imag__((float complex)z))
 #define cimagl(z) ((long double)__imag__((long double complex)z))
 
+// Function definitions of this form "type (name)(args)" are intentional, to
+// prevent macro versions of "name" from being incorrectly expanded. These
+// functions are here to provide external linkage to their macro implementations.
+
+// https://pubs.opengroup.org/onlinepubs/9699919799/functions/creal.html
+inline float(crealf)(float complex z)
+{
+    return crealf(z);
+}
+
+inline double(creal)(double complex z)
+{
+    return creal(z);
+}
+
+inline long double(creall)(long double complex z)
+{
+    return creall(z);
+}
+
+// https://pubs.opengroup.org/onlinepubs/9699919799/functions/cimag.html
+inline double(cimag)(double complex z)
+{
+    return cimag(z);
+}
+
+inline float(cimagf)(float complex z)
+{
+    return cimagf(z);
+}
+
+inline long double(cimagl)(long double complex z)
+{
+    return cimagl(z);
+}
+
 __END_DECLS