Fix test failure on systems with libstdc++ corresponding to gcc7.

This fixes #664.

As reported by @jirislaby the `test/Feature/LongDouble.cpp` test
fails to compile with Clang 3.4 due to new changes the libstdc++
headers. This ends up giving errors like

```
In file included from /home/abuild/rpmbuild/BUILD/klee-1.3.0+20170409/test/Feature/LongDouble.cpp:12:
In file included from /usr/bin/../lib64/gcc/x86_64-suse-linux/7/../../../../include/c++/7/cstdlib:77:
/usr/bin/../lib64/gcc/x86_64-suse-linux/7/../../../../include/c++/7/bits/std_abs.h:101:3: error: unknown type name '__float128'
  __float128
  ^
/usr/bin/../lib64/gcc/x86_64-suse-linux/7/../../../../include/c++/7/bits/std_abs.h:102:7: error: unknown type name '__float128'
  abs(__float128 __x)
      ^
2 errors generated.
```

Clang 4.0 seems fine with this source file so the problem has already
been addressed upstream so we don't need to file a bug. We just need
to move to a newer LLVM version to fix this properly!

To work around this the test has been made into a C program rather than
a C++ program to avoid including the C++ headers. The program wasn't
using any important C++ features anyway so this seems like a sensible change.

1 files changed, 61 insertions, 0 deletions

diff --git a/test/Feature/LongDouble.c b/test/Feature/LongDouble.c
new file mode 100644
index 00000000..ad4c1a79
--- /dev/null
+++ b/test/Feature/LongDouble.c
@@ -0,0 +1,61 @@
+// RUN: %llvmgcc  -g -emit-llvm -O0 -c -o %t.bc %s
+// RUN: rm -rf %t.klee-out
+// RUN: %klee --output-dir=%t.klee-out --libc=klee --no-output --exit-on-error %t.bc > %t.log
+// FIXME: When we remove LLVM 2.9 support just use FileCheck and remove these `grep`s.
+// RUN: grep -q powl\(-11\\.0,0\)=1\\.0\\+ %t.log
+// RUN: grep -q powl\(-11\\.0,1\)=-11\\.0\\+ %t.log
+// RUN: grep -q powl\(-11\\.0,2\)=121\\.0\\+ %t.log
+// RUN: grep -q 1/0=inf %t.log
+// RUN: grep -q 1/-1=-1\\.0\\+ %t.log
+// RUN: grep -q 1/-2=-0\\.50\\+ %t.log
+
+#include "klee/klee.h"
+#include <assert.h>
+#include <math.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+unsigned klee_urange(unsigned start, unsigned end) {
+  unsigned x;
+  klee_make_symbolic(&x, sizeof x, "x");
+  if (x - start >= end - start)
+    klee_silent_exit(0);
+  return x;
+}
+
+int main(int argc, char **argv) {
+  int a = klee_urange(0, 3);
+  int b;
+
+  // fork states
+  switch (a) {
+  case 0:
+    b = -0;
+    break;
+  case 1:
+    b = -1;
+    break;
+  case 2:
+    b = -2;
+    break;
+  default:
+    assert(0 && "Impossible switch target");
+  }
+
+  // test 80-bit external dispatch
+  long double d = powl((long double)-11.0, (long double)a);
+  // FIXME: Use CHECK-DAG: with FileCheck tool
+  // CHECK-DAG: powl(-11.0,0)=1.0
+  // CHECK-DAG: powl(-11.0,1)=-11.0
+  // CHECK-DAG: powl(-11.0,2)=121.0
+  printf("powl(-11.0,%d)=%Lf\n", a, d);
+
+  // test 80-bit fdiv
+  long double e = (long double)1 / (long double)b;
+  // CHECK-DAG: 1/0=inf
+  // CHECK-DAG: 1/1-1=-1.0
+  // CHECK-DAG: 1/-2=-0.50
+  printf("1/%d=%Lf\n", b, e);
+
+  return 0;
+}