Add initial FreeBSD support (#1430)

Add initial FreeBSD support

resources/examples/nolibc-freebsd/hello_world.c3

@@ -0,0 +1,22 @@
+fn int main()
+{
+    String msg = "Hello, C3 World!\n";
+    $$syscall(4, 1, (uptr)msg.ptr, msg.len); // __NR_write, STDOUT
+    return 0;
+}
+
+fn void _start() @export("_start")
+{
+    int ret = main();
+    $$syscall(1, ret); // __NR_exit
+}
+
+module std::core::builtin;
+
+def PanicFn = fn void(String message, String file, String function, uint line);
+
+PanicFn panic = &default_panic;
+
+fn void default_panic(String message, String file, String function, uint line)
+{
+}

resources/examples/nolibc-freebsd/project.json

@@ -0,0 +1,79 @@
+{
+  // Language version of C3.
+  "langrev": "1",
+  // Warnings used for all targets.
+  "warnings": [ "no-unused" ],
+  // Directories where C3 library files may be found.
+  "dependency-search-paths": [ ],
+  // Libraries to use for all targets.
+  "dependencies": [ ],
+  // Authors, optionally with email.
+  "authors": [ "John Doe <john.doe@example.com>" ],
+  // Version using semantic versioning.
+  "version": "0.1.0",
+  // Sources compiled for all targets.
+  "sources": [ "./**" ],
+  // C sources if the project also compiles C sources
+  // relative to the project file.
+  // "c-sources": [ "csource/**" ],
+  // Output location, relative to project file.
+  "output": ".",
+  // Architecture and OS target.
+  // You can use 'c3c --list-targets' to list all valid targets.
+  "target": "freebsd-x64",
+  // Targets.
+  "targets": {
+    "hello_world": {
+      "type": "executable",
+      "debug-info": "none",
+      "link-libc": false,
+      "opt": "O0",
+      "safe": false,
+      "linker": "builtin",
+      "use-stdlib": false,
+    },
+  },
+  // Global settings.
+  // C compiler if the project also compiles C sources
+  // defaults to 'cc'.
+  "cc": "cc",
+  // CPU name, used for optimizations in the LLVM backend.
+  "cpu": "generic",
+  // Debug information, may be "none", "full" and "line-tables".
+  "debug-info": "full",
+  // FP math behaviour: "strict", "relaxed", "fast".
+  "fp-math": "strict",
+  // Link libc other default libraries.
+  "link-libc": true,
+  // Memory environment: "normal", "small", "tiny", "none".
+  "memory-env": "normal",
+  // Optimization: "O0", "O1", "O2", "O3", "O4", "O5", "Os", "Oz".
+  "opt": "O0",
+  // Code optimization level: "none", "less", "more", "max".
+  "optlevel": "none",
+  // Code size optimization: "none", "small", "tiny".
+  "optsize": "none",
+  // Relocation model: "none", "pic", "PIC", "pie", "PIE".
+  "reloc": "none",
+  // Trap on signed and unsigned integer wrapping for testing.
+  "trap-on-wrap": false,
+  // Turn safety (contracts, runtime bounds checking, null pointer checks etc).
+  "safe": true,
+  // Compile all modules together, enables more inlining.
+  "single-module": true,
+  // Use / don't use soft float, value is otherwise target default.
+  "soft-float": false,
+  // Strip unused code and globals from the output.
+  "strip-unused": true,
+  // The size of the symtab, which limits the amount
+  // of symbols that can be used. Should usually not be changed.
+  "symtab": 1048576,
+  // Select linker.
+  "linker": "cc",
+  // Include the standard library.
+  "use-stdlib": true,
+  // Set general level of x64 cpu: "baseline", "ssse3", "sse4", "avx1", "avx2-v1", "avx2-v2", "avx512", "native".
+  "x86cpu": "native",
+  // Set max type of vector use: "none", "mmx", "sse", "avx", "avx512", "native".
+  "x86vec": "sse",
+}