fix a pal build issue on my machine

Not sure why it does not repro in CI. Maybe my system is updated?

finite.cpp includes "pal_internal.h -> pal.h" and has "wchar_t" defined.
finite.cpp then includes "math.h -> cmath -> bits/cpp_type_traits.h".
This results in error, _is_integer<> specialization duplicated on
"__wchar_16_cpp__ (expanded from wchar_t, and typedef to char16_t)"
and "char16_t".

Temporarily applied a local fix in finite.cpp.

Author: Jianchun Xu

pal/src/cruntime/finite.cpp

@@ -1,6 +1,6 @@
 //
 // Copyright (c) Microsoft. All rights reserved.
-// Licensed under the MIT license. See LICENSE file in the project root for full license information. 
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
 //
 
 /*++
@@ -21,7 +21,15 @@ Module Name:
 
 #include "pal/palinternal.h"
 #include "pal/dbgmsg.h"
+
+#if defined(__cplusplus)
+#undef wchar_t
+#endif
 #include <math.h>
+#if defined(__cplusplus)
+#undef wchar_t
+#define wchar_t __wchar_16_cpp__
+#endif // __cplusplus
 
 #if HAVE_IEEEFP_H
 #include <ieeefp.h>
@@ -98,8 +106,8 @@ _isnan(
 
 See MSDN doc
 --*/
-double 
-__cdecl 
+double
+__cdecl
 _copysign(
           double x,
           double y)
@@ -246,7 +254,7 @@ PALIMPORT double __cdecl PAL_exp(double x)
     PERF_ENTRY(exp);
     ENTRY("exp (x=%f)\n", x);
 #if !HAVE_COMPATIBLE_EXP
-    if (x == 1.0) 
+    if (x == 1.0)
     {
         ret = M_E;
     }
@@ -274,8 +282,8 @@ PALIMPORT LONG __cdecl PAL_labs(LONG l)
 
     PERF_ENTRY(labs);
     ENTRY("labs (l=%ld)\n", l);
-    
-    lRet = labs(l);    
+
+    lRet = labs(l);
 
     LOGEXIT("labs returns long %ld\n", lRet);
     PERF_EXIT(labs);