Add GCC backend using libgccjit

CMakeLists.txt

@@ -577,6 +577,8 @@ set(ZIG_STAGE2_SOURCES
     src/codegen/spirv/Module.zig
     src/codegen/spirv/Section.zig
     src/codegen/spirv/spec.zig
+    src/codegen/gccjit.zig
+    src/codegen/gccjit/bindings.zig
     src/crash_report.zig
     src/dev.zig
     src/glibc.zig

src/Compilation/Config.zig

@@ -103,6 +103,7 @@ pub const Options = struct {
     use_lib_llvm: ?bool = null,
     use_lld: ?bool = null,
     use_clang: ?bool = null,
+    use_gccjit: ?bool = null,
     lto: ?LtoMode = null,
     /// WASI-only. Type of WASI execution model ("command" or "reactor").
     wasi_exec_model: ?std.builtin.WasiExecModel = null,

src/codegen/gccjit.zig

@@ -0,0 +1,40 @@
+// Mostly copied from llvm.zig
+const std = @import("std");
+const builtin = @import("builtin");
+const assert = std.debug.assert;
+const Allocator = std.mem.Allocator;
+const log = std.log.scoped(.codegen);
+const math = std.math;
+const DW = std.dwarf;
+
+//const Builder = @import("llvm/Builder.zig");
+const gccjit = @import("gccjit/bindings.zig");
+const link = @import("../link.zig");
+const Compilation = @import("../Compilation.zig");
+const build_options = @import("build_options");
+const Zcu = @import("../Zcu.zig");
+const InternPool = @import("../InternPool.zig");
+const Package = @import("../Package.zig");
+const Air = @import("../Air.zig");
+const Liveness = @import("../Liveness.zig");
+const Value = @import("../Value.zig");
+const Type = @import("../Type.zig");
+const x86_64_abi = @import("../arch/x86_64/abi.zig");
+const wasm_c_abi = @import("../arch/wasm/abi.zig");
+const aarch64_c_abi = @import("../arch/aarch64/abi.zig");
+const arm_c_abi = @import("../arch/arm/abi.zig");
+const riscv_c_abi = @import("../arch/riscv64/abi.zig");
+const mips_c_abi = @import("../arch/mips/abi.zig");
+const dev = @import("../dev.zig");
+
+const Error = error{ OutOfMemory, CodegenFail };
+
+pub fn getGCCJIT_Type_FromInst(inst: Air.Inst.Ref) c_int {
+    switch (inst) {
+        .c_long_type => {
+            return gccjit.GCC_JIT_TYPE_LONG;
+        },
+
+        else => return 9,
+    }
+}