reorganized libcxx headers and replaced __abs_overloads and __cmath_type_traits to improve maintainability

Author: ZERICO2005

src/libc/include/__math_def.h

@@ -139,12 +139,9 @@ double      expm1(double);
 float       expm1f(float);
 long double expm1l(long double);
 
-#ifndef _ABS_FLOAT_DEFINED
-#define _ABS_FLOAT_DEFINED
 double      fabs(double);
 float       fabsf(float);
 long double fabsl(long double);
-#endif /* _ABS_FLOAT_DEFINED */
 
 double      fdim(double, double);
 float       fdimf(float, float);

src/libc/include/math.h

@@ -1,14 +1,10 @@
 #ifndef _MATH_H
 #define _MATH_H
 
-#ifdef __cplusplus
-
-#include <cmath>
-
-#else /* __cplusplus */
-
 #include <__math_def.h>
 
+#ifndef __cplusplus
+
 static inline __attribute__((__always_inline__))
 bool __signbitf(float __x) {
     if (__builtin_constant_p(__x)) {

src/libc/include/stdio.h

@@ -133,49 +133,4 @@ void perror(const char *str);
 
 __END_DECLS
 
-#ifdef __cplusplus
-namespace std {
-using ::size_t;
-using ::FILE;
-
-using ::fopen;
-using ::freopen;
-using ::fclose;
-using ::fflush;
-using ::ferror;
-using ::feof;
-using ::clearerr;
-using ::fread;
-using ::fwrite;
-using ::ftell;
-using ::fseek;
-using ::rewind;
-using ::fgetc;
-using ::fgets;
-using ::ungetc;
-using ::fputc;
-using ::fputs;
-using ::remove;
-using ::rename;
-using ::getchar;
-using ::putchar;
-using ::puts;
-using ::getc;
-using ::putc;
-using ::printf;
-using ::vprintf;
-using ::sprintf;
-using ::vsprintf;
-using ::snprintf;
-using ::vsnprintf;
-using ::fprintf;
-using ::vfprintf;
-using ::asprintf;
-using ::vasprintf;
-using ::sscanf;
-using ::vsscanf;
-using ::perror;
-} /* namespace std */
-#endif /* __cplusplus */
-
 #endif /* _STDIO_H */

src/libc/include/stdlib.h

@@ -104,9 +104,6 @@ void quick_exit(int) __NOEXCEPT __attribute__((noreturn));
 
 void _Exit(int) __NOEXCEPT __attribute__((noreturn));
 
-#ifndef _ABS_INT_DEFINED
-#define _ABS_INT_DEFINED
-
 int abs(int n);
 long labs(long n);
 long long llabs(long long n);
@@ -115,8 +112,6 @@ long long llabs(long long n);
 signed __int48 i48abs(signed __int48 n) __NOEXCEPT_CONST;
 #endif /* __SIZEOF_INT48__ */
 
-#endif /* _ABS_INT_DEFINED */
-
 div_t div(int numer, int denom);
 
 ldiv_t ldiv(long numer, long denom);