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/s_fminf.c b/libm/upstream-freebsd/lib/msun/src/s_fminf.c
index 2583167..58b6a48 100644
--- a/libm/upstream-freebsd/lib/msun/src/s_fminf.c
+++ b/libm/upstream-freebsd/lib/msun/src/s_fminf.c
@@ -33,6 +33,13 @@
 
 #include "fpmath.h"
 
+#ifdef USE_BUILTIN_FMINF
+float
+fminf(float x, float y)
+{
+	return (__builtin_fminf(x, y));
+}
+#else
 float
 fminf(float x, float y)
 {
@@ -53,3 +60,4 @@
 
 	return (x < y ? x : y);
 }
+#endif