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_hypotl.c b/libm/upstream-freebsd/lib/msun/src/e_hypotl.c
index 9189b1f..fc43538 100644
--- a/libm/upstream-freebsd/lib/msun/src/e_hypotl.c
+++ b/libm/upstream-freebsd/lib/msun/src/e_hypotl.c
@@ -82,7 +82,7 @@
 	        man_t manh, manl;
 		GET_LDBL_MAN(manh,manl,b);
 		if((manh|manl)==0) return a;
-		t1=0;
+		t1=1;
 		SET_HIGH_WORD(t1,ESW(MAX_EXP-2));	/* t1=2^(MAX_EXP-2) */
 		b *= t1;
 		a *= t1;