Fix ldexp builtin with vectors

In a few places we were always looking at component 0, which obviously
doesn't go well.

Bug: b/140648938
Test: dEQP-VK.*ldexp*
Change-Id: I6a8698a56beab8ccc3b41a729d399b957cde9495
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/36113
Tested-by: Chris Forbes <chrisforbes@google.com>
Presubmit-Ready: Chris Forbes <chrisforbes@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>

Author: chrisforbes

src/Pipeline/SpirvShader.cpp

@@ -4229,7 +4229,7 @@ namespace sw
 				auto in = significand.Float(i);
 				auto significandExponent = Exponent(in);
 				auto combinedExponent = exponent.Int(i) + significandExponent;
-				auto isSignificandZero     = SIMD::UInt(CmpEQ(significand.Int(0), SIMD::Int(0)));
+				auto isSignificandZero     = SIMD::UInt(CmpEQ(significand.Int(i), SIMD::Int(0)));
 				auto isSignificandInf      = SIMD::UInt(IsInf(in));
 				auto isSignificandNaN      = SIMD::UInt(IsNan(in));
 				auto isExponentNotTooSmall = SIMD::UInt(CmpGE(combinedExponent, SIMD::Int(-126)));
@@ -4247,7 +4247,7 @@ namespace sw
 				// If the input significand is zero, inf or nan, just return the
 				// input significand.
 				auto passthrough = isSignificandZero | isSignificandInf | isSignificandNaN;
-				v = (v & ~passthrough) | (significand.UInt(0) & passthrough);
+				v = (v & ~passthrough) | (significand.UInt(i) & passthrough);
 
 				dst.move(i, As<SIMD::Float>(v));
 			}