[libc++] Always build with -fvisibility=hidden

Summary:
This avoids symbols being accidentally exported from the dylib when they
shouldn't. The next step is to use a pragma to apply hidden visibility
to all declarations (unless otherwise specified), which will allow us
to drop the per-declaration hidden visibility attributes we currently
have.

This also has the nice side effect of making sure the dylib exports the
same symbols regardless of the optimization level.

PR38138

Reviewers: EricWF, mclow.lists

Subscribers: mgorny, christof, jkorous, dexonsmith, libcxx-commits

Tags: #libc

Differential Revision: https://reviews.llvm.org/D62868

llvm-svn: 368703
Cr-Mirrored-From: sso://chromium.googlesource.com/_direct/external/github.com/llvm/llvm-project
Cr-Mirrored-Commit: 8a033a9e3fb96b9a1099325c4cd218c1c979d9d9
diff --git a/src/valarray.cpp b/src/valarray.cpp
index 7bf0b41..64d2658 100644
--- a/src/valarray.cpp
+++ b/src/valarray.cpp
@@ -12,8 +12,8 @@
 
 // These two symbols are part of the v1 ABI but not part of the >=v2 ABI.
 #if _LIBCPP_ABI_VERSION == 1
-template valarray<size_t>::valarray(size_t);
-template valarray<size_t>::~valarray();
+template _LIBCPP_FUNC_VIS valarray<size_t>::valarray(size_t);
+template _LIBCPP_FUNC_VIS valarray<size_t>::~valarray();
 #endif
 
 template void valarray<size_t>::resize(size_t, size_t);