Fix incompatibilities with open-source Bazel-based build

- Add fall-backs for Clang-specific __builtin_shufflevector
- Make definition of XNN_UNPREDICTABLE compatible with GCC
- Add missing SIMD bitcasts in SSE PReLU micro-kernel
- Fix FP16 include paths in benchmarks
- Fix GTest include path in generated tests
- Fully qualify std::signbit and std::isnan

PiperOrigin-RevId: 272243695
diff --git a/test/prelu-microkernel-tester.h b/test/prelu-microkernel-tester.h
index d71f20c..3e773b4 100644
--- a/test/prelu-microkernel-tester.h
+++ b/test/prelu-microkernel-tester.h
@@ -9,6 +9,7 @@
 
 #include <algorithm>
 #include <cassert>
+#include <cmath>
 #include <cstddef>
 #include <cstdlib>
 #include <functional>
@@ -136,7 +137,7 @@
 
       // Compute reference results, without clamping.
       for (size_t i = 0; i < n(); i++) {
-        y_ref[i] = signbit(x_data[i]) ? x_data[i] * w[i] : x_data[i];
+        y_ref[i] = std::signbit(x_data[i]) ? x_data[i] * w[i] : x_data[i];
       }
 
       // Compute clamping parameters.