[driver][darwin] Don't use -platform_version flag by default (PR44813)

The code in llvmorg-10-init-12188-g25ce33a6e4f is a breaking change for
users of older linkers who don't pass a version parameter, which
prevents a drop-in clang upgrade. Old tools can't know about what future
tools will do, so as a general principle the burden should be new tools
to be compatible by default. Also, for comparison, none of the other
tests of Version within AddLinkArgs add any new behaviors unless the
version is explicitly specified. Therefore, this patch changes the
-platform_version behavior from opt-out to opt-in.

Patch by David Major!

Differential revision: https://reviews.llvm.org/D74784

(cherry picked from commit 5122e828701c88f8d53ee881bc68f3904454d154)

1 files changed, 1 insertions, 1 deletions

diff --git a/clang/lib/Driver/ToolChains/Darwin.cpp b/clang/lib/Driver/ToolChains/Darwin.cpp
index 344a14fe1ea..220bc8f9835 100644
--- a/clang/lib/Driver/ToolChains/Darwin.cpp
+++ b/clang/lib/Driver/ToolChains/Darwin.cpp
@@ -335,7 +335,7 @@ void darwin::Linker::AddLinkArgs(Compilation &C, const ArgList &Args,
   Args.AddAllArgs(CmdArgs, options::OPT_init);
 
   // Add the deployment target.
-  if (!Version[0] || Version[0] >= 520)
+  if (Version[0] >= 520)
     MachOTC.addPlatformVersionArgs(Args, CmdArgs);
   else
     MachOTC.addMinVersionArgs(Args, CmdArgs);