[libc] Add Int<> type and fix (U)Int<128> compatibility issues.

Add Int<> and Int128 types to replace the usage of __int128_t in math
functions.  Clean up to make sure that (U)Int128 and __(u)int128_t are
interchangeable in the code base.

Reviewed By: sivachandra, mikhail.ramalho

Differential Revision: https://reviews.llvm.org/D152459

libc/src/__support/CMakeLists.txt

@@ -134,6 +134,7 @@ add_header_library(
     libc.src.__support.FPUtil.fenv_impl
     libc.src.__support.FPUtil.fp_bits
     libc.src.__support.FPUtil.rounding_mode
+    libc.src.__support.FPUtil.dyadic_float
     libc.src.__support.builtin_wrappers
     libc.src.__support.common
     libc.src.errno.errno

libc/src/__support/FPUtil/generic/sqrt.h

@@ -137,7 +137,7 @@ LIBC_INLINE cpp::enable_if_t<cpp::is_floating_point_v<T>, T> sqrt(T x) {
       }
 
       // We compute one more iteration in order to round correctly.
-      bool lsb = y & 1; // Least significant bit
+      bool lsb = static_cast<bool>(y & 1); // Least significant bit
       bool rb = false;  // Round bit
       r <<= 2;
       UIntType tmp = (y << 2) + 1;

libc/src/__support/FPUtil/generic/sqrt_80_bit_long_double.h

@@ -101,7 +101,7 @@ LIBC_INLINE long double sqrt(long double x) {
     }
 
     // We compute one more iteration in order to round correctly.
-    bool lsb = y & 1; // Least significant bit
+    bool lsb = static_cast<bool>(y & 1); // Least significant bit
     bool rb = false;  // Round bit
     r <<= 2;
     UIntType tmp = (y << 2) + 1;

libc/src/__support/FPUtil/x86_64/LongDoubleBits.h

@@ -130,6 +130,10 @@ template <> struct FPBits<long double> {
     return bits & MASK;
   }
 
+  LIBC_INLINE long double get_val() const {
+    return cpp::bit_cast<long double>(bits);
+  }
+
   LIBC_INLINE int get_exponent() const {
     if (get_unbiased_exponent() == 0)
       return int(1) - EXPONENT_BIAS;