stdlib: qsort and bsearch changes.

- Always use internal qsort and bsearch implementation.
- add "_r" reentrant versions.

The reasons for always using the internal versions is that the C runtime
versions' callbacks are not mark STDCALL, so we would have add bridge
functions for them anyhow, The C runtime qsort_r/qsort_s have different
orders of arguments on different platforms, and most importantly: qsort()
isn't a stable sort, and isn't guaranteed to give the same ordering for
two objects marked as equal by the callback...as such, Visual Studio and
glibc can give different sort results for the same data set...in this
sense, having one piece of code shared on all platforms makes sense here,
for reliabillity.

bsearch does not have a standard _r version at all, and suffers from the
same SDLCALL concern. Since the code is simple and we would have to work
around the C runtime, it's easier to just go with the built-in function
and remove all the CMake C runtime tests.

Fixes #9159.

CMakeLists.txt

@@ -1058,7 +1058,7 @@ if(SDL_LIBC)
 
   set(symbols_to_check
     abs acos acosf asin asinf atan atan2 atan2f atanf atof atoi
-    bcopy bsearch
+    bcopy
     calloc ceil ceilf copysign copysignf cos cosf
     _Exit exp expf
     fabs fabsf floor floorf fmod fmodf fopen64 free fseeko fseeko64
@@ -1067,7 +1067,6 @@ if(SDL_LIBC)
     log log10 log10f logf lround lroundf _ltoa
     malloc memcmp memcpy memmove memset modf modff
     pow powf putenv
-    qsort
     realloc rindex round roundf
     scalbn scalbnf setenv sin sinf sqr sqrt sqrtf sscanf strchr
     strcmp strlcat strlcpy strlen strncmp strnlen