Prevent redefinition of WCHAR_MAX from testsuite/gcc.dg/cpp/ucs.c

gcc/testsuite/gcc.dg/cpp/ucs.c #include <limits.h>
and then crafts a definition of WCHAR_MAX depending
on __WCHAR_TYPE__.

The test fails in VxWorks configurations because WCHAR_MAX
is already exposed by the system limits.h.

The patch simply guards the tentative definition
by a check verifying if the macro is defined already, so
we're using the value exposed by limits.h in this case.

2019-12-30  Olivier Hainque  <hainque@adacore.com>

	* testsuite/gcc.dg/cpp/ucs.c: Prevent redefinition
	of WCHAR_MAX if already exposed by limits.h.

From-SVN: r279795

gcc/testsuite/ChangeLog

 2019-12-20  Olivier Hainque  <hainque@adacore.com>
+
+	* testsuite/gcc.dg/cpp/ucs.c: Prevent redefinition
+	of WCHAR_MAX if already exposed by limits.h.
+
+2019-12-20  Olivier Hainque  <hainque@adacore.com>
            Jerome Lambourg  <lambourg@adacore.com>
 
 	* c-c++-common/pr56493.c: Allow '$' in addition to '.'

gcc/testsuite/gcc.dg/cpp/ucs.c

@@ -16,6 +16,8 @@
 #define short           +2 
 #define long            +3
 
+#if !defined(WCHAR_MAX)
+
 #if __WCHAR_TYPE__ == 0
 # define WCHAR_MAX      INT_MAX
 #elif __WCHAR_TYPE__ == 1
@@ -28,6 +30,8 @@
 # error wacky wchar_t
 #endif
 
+#endif
+
 #undef unsigned
 #undef int
 #undef char