CRuntime_Musl: Support v1.2.0 for 32 bits

As explained in the comment, `time_t` on Musl is now always 64 bits,
but used to be 32 bits on 32 bits systems.

changelog/musl-32bits.dd

@@ -0,0 +1,11 @@
+Support time64 changes for `CRuntime_Musl`
+
+Up to v1.1.24, Musl used a 32 bits `time_t` on 32 bits architectures.
+Since v1.2.0, `time_t` is now always 64 bits.
+From this release, druntime will also default to a 64 bits `time_t`
+on 32 bits architecture, unless the `CRuntime_Musl_Pre_Time64w` is provided.
+
+This change should only affect packagers for Musl-based systems who support
+32 bits architectures (64 bits architectures already use 64 bits `time_t`),
+who now need to define `CRuntime_Musl_Pre_Time64` both when building
+druntime / Phobos and in the default configuration, if the linked Musl is < 1.2.0.