fix gcc problems

Author: bassiounix

libc/src/__support/FPUtil/multiply_add.h

@@ -29,7 +29,7 @@ multiply_add(const T &x, const T &y, const T &z) {
 }
 
 template <typename T>
-LIBC_INLINE cpp::enable_if_t<(sizeof(T) <= sizeof(void *)), T>
+LIBC_INLINE static constexpr cpp::enable_if_t<(sizeof(T) <= sizeof(void *)), T>
 multiply_add(T x, T y, T z) {
   return x * y + z;
 }

libc/src/__support/FPUtil/nearest_integer.h

@@ -40,7 +40,7 @@ namespace fputil {
 // Notice that for AARCH64 and x86-64 with SSE4.2 support, we will use their
 // corresponding rounding instruction instead.  And in those cases, the results
 // are rounded to the nearest integer, tie-to-even.
-LIBC_INLINE float nearest_integer(float x) {
+LIBC_INLINE static constexpr float nearest_integer(float x) {
   if (x < 0x1p24f && x > -0x1p24f) {
     float r = x < 0 ? (x - 0x1.0p23f) + 0x1.0p23f : (x + 0x1.0p23f) - 0x1.0p23f;
     float diff = x - r;
@@ -56,7 +56,7 @@ LIBC_INLINE float nearest_integer(float x) {
   return x;
 }
 
-LIBC_INLINE double nearest_integer(double x) {
+LIBC_INLINE static constexpr double nearest_integer(double x) {
   if (x < 0x1p53 && x > -0x1p53) {
     double r = x < 0 ? (x - 0x1.0p52) + 0x1.0p52 : (x + 0x1.0p52) - 0x1.0p52;
     double diff = x - r;

libc/src/__support/math/expf16_utils.h

@@ -47,7 +47,7 @@ struct ExpRangeReduction {
   float exp_lo;
 };
 
-static constexpr ExpRangeReduction exp_range_reduction(float16 x) {
+[[maybe_unused]] static ExpRangeReduction exp_range_reduction(float16 x) {
   // For -18 < x < 12, to compute exp(x), we perform the following range
   // reduction: find hi, mid, lo, such that:
   //   x = hi + mid + lo, in which