intrinsic-test: Print C++ float16_t in hex

Upstream Rust currently does not support printing f16s in decimal.
For the intrinsics tests to work, make C++ print float16_t in the same
format.

Can be droppen once rust-lang/rust#127013
is merged.

Author: mrkajetanp

crates/intrinsic-test/missing_aarch64.txt

@@ -27,3 +27,6 @@ vrnd64z_f64
 
 # Broken in Clang
 vcvth_s16_f16
+# FIXME: Broken output due to missing f16 printing support in Rust, see git blame for this line
+vmulh_lane_f16
+vmulh_laneq_f16

crates/intrinsic-test/src/main.rs

@@ -114,6 +114,15 @@ std::ostream& operator<<(std::ostream& os, poly128_t value) {{
 }}
 #endif
 
+std::ostream& operator<<(std::ostream& os, float16_t value) {{
+    uint16_t temp = 0;
+    memcpy(&temp, &value, sizeof(float16_t));
+    std::stringstream ss;
+    ss << "0x" << std::setfill('0') << std::setw(4) << std::hex << temp;
+    os << ss.str();
+    return os;
+}}
+
 {arglists}
 
 int main(int argc, char **argv) {{