compiler-rt, zigc: Use hidden visibility except when testing.

This prevents symbols from these libraries from polluting the dynamic symbol
tables of binaries built with Zig. The downside is that we no longer deduplicate
the symbols at run time due to weak linkage.

Closes #7935.
Closes #13303.
Closes #19342.

Author: alexrp

lib/c/common.zig

@@ -9,7 +9,7 @@ else
 /// Determines the symbol's visibility to other objects.
 /// For WebAssembly this allows the symbol to be resolved to other modules, but will not
 /// export it to the host runtime.
-pub const visibility: std.builtin.SymbolVisibility = if (builtin.cpu.arch.isWasm() and linkage != .internal)
+pub const visibility: std.builtin.SymbolVisibility = if (linkage != .internal)
     .hidden
 else
     .default;

lib/compiler_rt/common.zig

@@ -13,8 +13,10 @@ else
 /// Determines the symbol's visibility to other objects.
 /// For WebAssembly this allows the symbol to be resolved to other modules, but will not
 /// export it to the host runtime.
-pub const visibility: std.builtin.SymbolVisibility =
-    if (builtin.target.cpu.arch.isWasm() and linkage != .internal) .hidden else .default;
+pub const visibility: std.builtin.SymbolVisibility = if (linkage != .internal)
+    .hidden
+else
+    .default;
 
 pub const PreferredLoadStoreElement = element: {
     if (std.simd.suggestVectorLength(u8)) |vec_size| {