cortex-m0plus and fix for missing hal (#49)

src/core/microzig.zig

@@ -24,6 +24,8 @@ pub const board = if (config.has_board) @import("board") else void;
 /// Provides access to the low level features of the CPU.
 pub const cpu = @import("cpu");
 
+pub const hal = @import("hal");
+
 /// Module that helps with interrupt handling.
 pub const interrupts = @import("interrupts.zig");
 

src/modules/cpus.zig

@@ -18,6 +18,17 @@ pub const avr5 = Cpu{
     },
 };
 
+pub const cortex_m0plus = Cpu{
+    .name = "ARM Cortex-M0+",
+    .path = root_path ++ "cpus/cortex-m/cortex-m.zig",
+    .target = std.zig.CrossTarget{
+        .cpu_arch = .thumb,
+        .cpu_model = .{ .explicit = &std.Target.arm.cpu.cortex_m0plus },
+        .os_tag = .freestanding,
+        .abi = .none,
+    },
+};
+
 pub const cortex_m3 = Cpu{
     .name = "ARM Cortex-M3",
     .path = root_path ++ "cpus/cortex-m/cortex-m.zig",