libm: sync with upstream.

There's potential here to maybe lose some/all of builtins.cpp, but I'll
look at that separately later.

Test: treehugger
Change-Id: I2c2bc1d0753affdd214daeb09fa1ac7cd73db347
diff --git a/libm/upstream-freebsd/lib/msun/src/e_sqrtf.c b/libm/upstream-freebsd/lib/msun/src/e_sqrtf.c
index 7eba4d0..06e5d62 100644
--- a/libm/upstream-freebsd/lib/msun/src/e_sqrtf.c
+++ b/libm/upstream-freebsd/lib/msun/src/e_sqrtf.c
@@ -20,6 +20,13 @@
 #include "math.h"
 #include "math_private.h"
 
+#ifdef USE_BUILTIN_SQRTF
+float
+__ieee754_sqrtf(float x)
+{
+	return (__builtin_sqrtf(x));
+}
+#else
 static	const float	one	= 1.0, tiny=1.0e-30;
 
 float
@@ -87,3 +94,4 @@
 	SET_FLOAT_WORD(z,ix);
 	return z;
 }
+#endif