Driver: Turn the default value for -fmath-errno into a proper target hook and disable it by default on more platforms.

For now -fno-math-errno is the default on BSD-derived platforms (Darwin,
DragonFlyBSD, FreeBSD, NetBSD, OpenBSD). If the default is not right for
your platform, please yell. I only verified the result with the default
compilers on Darwin and FreeBSD.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@155990 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/test/Driver/fast-math.c b/test/Driver/fast-math.c
index 09d249d..8426f09 100644
--- a/test/Driver/fast-math.c
+++ b/test/Driver/fast-math.c
@@ -26,6 +26,14 @@
 // RUN:   | FileCheck --check-prefix=CHECK-NO-MATH-ERRNO %s
 // RUN: %clang -### -target i686-apple-darwin -c %s 2>&1 \
 // RUN:   | FileCheck --check-prefix=CHECK-NO-MATH-ERRNO %s
+// RUN: %clang -### -target x86_64-unknown-freebsd -c %s 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-NO-MATH-ERRNO %s
+// RUN: %clang -### -target x86_64-unknown-netbsd -c %s 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-NO-MATH-ERRNO %s
+// RUN: %clang -### -target x86_64-unknown-openbsd -c %s 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-NO-MATH-ERRNO %s
+// RUN: %clang -### -target x86_64-unknown-dragonfly -c %s 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-NO-MATH-ERRNO %s
 // CHECK-NO-MATH-ERRNO: "-cc1"
 // CHECK-NO-MATH-ERRNO-NOT: "-fmath-errno"
 //