check libc and arch in Linux build

These checks allow us to detect compilation on systems which
may not meet requirements for stat(2) struct field layout
and __xstat64() libc ABI support on Linux.

From microsoft/VFSForGit@5b1236c.

Scripts/Linux/BuildScalarForLinux.sh

@@ -12,6 +12,22 @@ if [ -z $VERSION ]; then
   VERSION="0.2.173.2"
 fi
 
+ARCH=$(uname -m)
+if test "$ARCH" != "x86_64"; then
+  >&2 echo "architecture must be x86_64 for struct stat; stopping"
+  exit 1
+fi
+
+CC=${CC:-cc}
+
+echo 'main(){int i=1;const char *n="n";struct stat b;i=__xstat64(i,n,&b);}' | \
+  cc -xc -include sys/stat.h -o /dev/null - 2>/dev/null
+
+if test $? != 0; then
+  >&2 echo "__xstat64() not found in libc ABI; stopping"
+  exit 1
+fi
+
 # If we're building the Profiling(Release) configuration, remove Profiling() for building .NET code
 if [ "$CONFIGURATION" == "Profiling(Release)" ]; then
   CONFIGURATION=Release