AK: Always use serenity's math routines, even in lagom builds

Some of the functions in AK/Math.h used to implement math routines if
AK_OS_SERENITY was defined, but called __builtin_foo() in lagom builds.

This was not done consistently. Many functions always implemented
math functions without this check, for example:

- copysign()
- acos(), asin()
- cosh(), sinh(), tanh(), acosh, asinh(), atanh()
- exp2(), log2(), pow()

Move the functions that did that check to not doing it as well.
This means these functions now use the same implementation in
serenity and lagom. Since lagom is for testing serenity code
outside serenity, this seems like a good change.

All these functions check for x86 for and use inline assembly
there, so this only affects non-x86 lagom builds. It affects
these functions:

- fmod()
- remainder() (now always a TODO(), not just in serenity)
- sin(), cos(), tan()
- atan(), atan2()
- log(), log10()

It changes but does not really affect sqrt() -- now a TODO() on non-x86
non-arm non-riscv lagom (i.e. nowhere).

As Serenity's implementations of these math functions are currently
lower-quality than what's usually in lagom libms, this regresses lagom
behavior (performance, precision) on non-x86 for these functions.
But only to the level they're at within serenity, and we'll have to
improve these functions there anyways.

Author: nico

AK/Math.h

@@ -439,7 +439,6 @@ constexpr T fmod(T x, T y)
     } while (fpu_status & 0x400);
     return x;
 #else
-#    if defined(AK_OS_SERENITY)
     // FIXME: This is a very naive implementation.
 
     if (__builtin_isnan(x))
@@ -526,14 +525,6 @@ constexpr T fmod(T x, T y)
     x_bits.exponent = x_exponent;
     x_bits.mantissa = x_mantissa;
     return x_bits.to_float();
-#    else
-    if constexpr (IsSame<T, long double>)
-        return __builtin_fmodl(x, y);
-    if constexpr (IsSame<T, double>)
-        return __builtin_fmod(x, y);
-    if constexpr (IsSame<T, float>)
-        return __builtin_fmodf(x, y);
-#    endif
 #endif
 }
 
@@ -553,16 +544,8 @@ constexpr T remainder(T x, T y)
     } while (fpu_status & 0x400);
     return x;
 #else
-#    if defined(AK_OS_SERENITY)
     // TODO: Add implementation for this function.
     TODO();
-#    endif
-    if constexpr (IsSame<T, long double>)
-        return __builtin_remainderl(x, y);
-    if constexpr (IsSame<T, double>)
-        return __builtin_remainder(x, y);
-    if constexpr (IsSame<T, float>)
-        return __builtin_remainderf(x, y);
 #endif
 }
 }
@@ -615,11 +598,8 @@ constexpr T sqrt(T x)
     if constexpr (IsSame<T, long double>)
         TODO_RISCV64();
 #else
-#    if defined(AK_OS_SERENITY)
     // TODO: Add implementation for this function.
     TODO();
-#    endif
-    return __builtin_sqrt(x);
 #endif
 }
 
@@ -684,7 +664,6 @@ constexpr T sin(T angle)
         : "0"(angle));
     return ret;
 #else
-#    if defined(AK_OS_SERENITY)
     T sign = 1;
     if (angle < 0) {
         angle = -angle;
@@ -726,9 +705,6 @@ constexpr T sin(T angle)
     };
     T angle_squared = angle * angle;
     return sign * (angle + angle * angle_squared * f(angle_squared));
-#    else
-    return __builtin_sin(angle);
-#    endif
 #endif
 }
 
@@ -745,7 +721,6 @@ constexpr T cos(T angle)
         : "0"(angle));
     return ret;
 #else
-#    if defined(AK_OS_SERENITY)
     if (angle < 0)
         angle = -angle;
 
@@ -789,9 +764,6 @@ constexpr T cos(T angle)
     };
     T angle_squared = angle * angle;
     return sign * (1 + angle_squared * f(angle_squared));
-#    else
-    return __builtin_cos(angle);
-#    endif
 #endif
 }
 
@@ -828,11 +800,7 @@ constexpr T tan(T angle)
 
     return ret;
 #else
-#    if defined(AK_OS_SERENITY)
     return sin(angle) / cos(angle);
-#    else
-    return __builtin_tan(angle);
-#    endif
 #endif
 }
 
@@ -898,10 +866,7 @@ constexpr T atan(T value)
         : "0"(value));
     return ret;
 #else
-#    if defined(AK_OS_SERENITY)
     return asin(value / sqrt(1 + value * value));
-#    endif
-    return __builtin_atan(value);
 #endif
 }
 
@@ -918,7 +883,6 @@ constexpr T atan2(T y, T x)
         : "st(1)");
     return ret;
 #else
-#    if defined(AK_OS_SERENITY)
     if (__builtin_isnan(y))
         return y;
     if (__builtin_isnan(x))
@@ -978,9 +942,6 @@ constexpr T atan2(T y, T x)
         return atan(y / x) - Pi<T>;
     // y < 0 && x > 0
     return atan(y / x);
-#    else
-    return __builtin_atan2(y, x);
-#    endif
 #endif
 }
 
@@ -1094,11 +1055,9 @@ constexpr T log(T x)
         : "=t"(ret)
         : "0"(x));
     return ret;
-#elif defined(AK_OS_SERENITY)
+#else
     // FIXME: Adjust the polynomial and formula in log2 to fit this
     return log2<T>(x) / L2_E<T>;
-#else
-    return __builtin_log(x);
 #endif
 }
 
@@ -1116,11 +1075,9 @@ constexpr T log10(T x)
         : "=t"(ret)
         : "0"(x));
     return ret;
-#elif defined(AK_OS_SERENITY)
+#else
     // FIXME: Adjust the polynomial and formula in log2 to fit this
     return log2<T>(x) / L2_10<T>;
-#else
-    return __builtin_log10(x);
 #endif
 }