Add parallel_build example

Author: rexim

how_to/005_parallel_build/.gitignore

@@ -0,0 +1,3 @@
+nob
+nob.old
+build/

how_to/005_parallel_build/nob.c

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+#define NOB_IMPLEMENTATION
+#define NOB_STRIP_PREFIX
+#include "nob.h"
+
+#define BUILD_FOLDER "build/"
+#define SRC_FOLDER "src/"
+
+int main(int argc, char **argv)
+{
+    NOB_GO_REBUILD_URSELF(argc, argv);
+
+    Cmd cmd = {0};
+    Procs procs = {0};
+
+    if (!mkdir_if_not_exists(BUILD_FOLDER)) return 1;
+
+    // Spawn three async processes collecting them to procs dynamic array
+    cmd_append(&cmd, "cc", "-o", BUILD_FOLDER"foo", SRC_FOLDER"foo.c");
+    da_append(&procs, cmd_run_async_and_reset(&cmd));
+    cmd_append(&cmd, "cc", "-o", BUILD_FOLDER"bar", SRC_FOLDER"bar.c");
+    da_append(&procs, cmd_run_async_and_reset(&cmd));
+    cmd_append(&cmd, "cc", "-o", BUILD_FOLDER"baz", SRC_FOLDER"baz.c");
+    da_append(&procs, cmd_run_async_and_reset(&cmd));
+
+    // Wait on all the async processes to finish
+    if (!procs_wait_and_reset(&procs)) return 1;
+
+    // TODO: add some examples with nob_procs_append_with_flush()
+
+    return 0;
+}

how_to/005_parallel_build/nob.h

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+../../nob.h

how_to/005_parallel_build/src/bar.c

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+#include <stdio.h>
+
+int main()
+{
+    printf("Bar\n");
+    return 0;
+}

how_to/005_parallel_build/src/baz.c

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+#include <stdio.h>
+
+int main()
+{
+    printf("Baz\n");
+    return 0;
+}

how_to/005_parallel_build/src/foo.c

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+#include <stdio.h>
+
+int main()
+{
+    printf("Foo\n");
+    return 0;
+}