MDEV-21082: isnan/isinf compilation errors, isfinite warnings on MacOS

The fix consists of three commits backported from 10.3:

1) Cleanup isnan() portability checks

(cherry picked from commit 7ffd7fe9627d1f750a3712aebb4503e5ae8aea8e)

2) Cleanup isinf() portability checks

Original problem reported by Wlad: re-compilation of 10.3 on top of 10.2
build would cache undefined HAVE_ISINF from 10.2, whereas it is expected
to be 1 in 10.3.

std::isinf() seem to be available on all supported platforms.
(cherry picked from commit bc469a0bdf85400f7a63834f5b7af1a513dcdec9)

3) Use std::isfinite in C++ code

This is addition to parent revision fixing build failures.

(cherry picked from commit 54999f4e75f42baca484ae436b382ca8817df1dd)

1 files changed, 3 insertions, 3 deletions

diff --git a/sql/field.cc b/sql/field.cc
index a23004ebd96..09e82acb009 100644
--- a/sql/field.cc
+++ b/sql/field.cc
@@ -2904,7 +2904,7 @@ int Field_decimal::store(double nr)
     return 1;
   }
   
-  if (!isfinite(nr)) // Handle infinity as special case
+  if (!std::isfinite(nr)) // Handle infinity as special case
   {
     overflow(nr < 0.0);
     return 1;
@@ -4821,7 +4821,7 @@ int truncate_double(double *nr, uint field_length, uint dec,
   int error= 0;
   double res= *nr;
   
-  if (isnan(res))
+  if (std::isnan(res))
   {
     *nr= 0;
     return -1;
@@ -4843,7 +4843,7 @@ int truncate_double(double *nr, uint field_length, uint dec,
     max_value-= 1.0 / log_10[dec];
 
     /* Check for infinity so we don't get NaN in calculations */
-    if (!my_isinf(res))
+    if (!std::isinf(res))
     {
       double tmp= rint((res - floor(res)) * log_10[dec]) / log_10[dec];
       res= floor(res) + tmp;