Fix the build system.

The improvements are:

- use most of the default "Makefile" for standard packaging;
- also use the default ".gitignore" with for the derived assets;
- don't impose so many $CFLAGS on the user.  GCC still needs to be given
  the `-ffreestanding` flag explicitly for us to get a good binary;
- stop using ad-hoc tools/* scripts, and avoid the code-generation
  anti-pattern overall on the build.  Some of the generated files were
  checked-in, and some were removed;
- remove empty files;
- use POSIX make(1) over gmake;
- add fuzz targets;
- partial "install" and "uninstall" targets;
- complete "clean" target.

The shortcomings are:
- only working on x86_64.  More platforms coming soon;
- code is still messy: way too many warnings, GNU/BSD specific
  extensions, inline assembly, and all kinds of unportable code;
- still only works with GCC and GCC-like compilers, and completly fails
  with tcc(1) and cproc(1);
- the `deps.mk` file is being maintained manually.  As I work on the
  source files I'll finish automating its generation with `mkdeps.sh`;
- still seems to be coupled with Linux;
- still is missing tests setup;
- still uses `#include <$NAME.h>` instead of the correct
  `#include "$NAME.h"` form.

The generated libgrovel.a did match the previous lib/libc.a 100%.

5 files changed, 4 insertions, 0 deletions

diff --git a/src/setjmp/longjmp.c b/src/config.h.in
index e69de29b..e69de29b 100644
--- a/src/setjmp/longjmp.c
+++ b/src/config.h.in
diff --git a/src/setjmp/setjmp.c b/src/grovel.h
index e69de29b..e69de29b 100644
--- a/src/setjmp/setjmp.c
+++ b/src/grovel.h
diff --git a/src/main.c b/src/main.c
new file mode 100644
index 00000000..1d658dd1
--- /dev/null
+++ b/src/main.c
@@ -0,0 +1,4 @@
+int
+main(void) {
+	return 0;
+}
diff --git a/src/signal/sigsetjmp.c b/src/signal/sigsetjmp.c
deleted file mode 100644
index e69de29b..00000000
--- a/src/signal/sigsetjmp.c
+++ /dev/null
diff --git a/src/thread/syscall_cp.c b/src/thread/syscall_cp.c
deleted file mode 100644
index e69de29b..00000000
--- a/src/thread/syscall_cp.c
+++ /dev/null