Reorganize .gitignore to make better use of its features

It's possible to have a very few rules for some directories and trust
that other patterns further along will take care of whatever is left.
.gitignore should therefore be loosely organised from least generic to
most generic, allowing things like this:

    # Keep any file with extensions, such as foo.c, bar.h, ...
    !/dir/*.*

    # ....

    # Remove all object files
    *.o
    *.obj

With this change, we implement some very generic rules for what will
and will not be ignored in the fuzz subdirectory, and truse that
patterns later on (such as *.o, *.obj, *.exe) will take care of
everything we didn't specifically specify for the fuzz subdirectory.
Reviewed-by: NRich Salz <rsalz@openssl.org>

.gitignore

-# Object files
-*.o
-*.obj
-
-# editor artefacts
-*.swp
-.#*
-\#*#
-*~
+# Ignore editor artefacts
 /.dir-locals.el
 
 # Top level excludes
@@ -25,56 +17,20 @@
 # *all* Makefiles
 Makefile
 
-/test/*.ss
-/test/*.srl
-/test/.rnd
-/test/test*.pem
-/test/newkey.pem
-/test/*.log
-/test/buildtest_*
-
-# Certificate symbolic links
-*.0
-
 # Links under apps
 /apps/CA.pl
 /apps/tsget
 /apps/tsget.pl
 /apps/md4.c
 
-
 # Auto generated headers
 /crypto/buildinf.h
 /crypto/include/internal/*_conf.h
 /openssl/include/opensslconf.h
 /util/domd
 
-# Auto generated assembly language source files
-*.s
-!/crypto/*/asm/*.s
-/crypto/arm*.S
-/crypto/*/*.S
-*.asm
-!/crypto/*/asm/*.asm
-
 # Executables
 /apps/openssl
-/fuzz/asn1
-/fuzz/asn1-test
-/fuzz/asn1parse
-/fuzz/asn1parse-test
-/fuzz/bignum
-/fuzz/bignum-test
-/fuzz/bndiv
-/fuzz/bndiv-test
-/fuzz/conf
-/fuzz/conf-test
-/fuzz/cms
-/fuzz/cms-test
-/fuzz/ct
-/fuzz/ct-test
-/fuzz/server
-/fuzz/server-test
 /test/sha256t
 /test/sha512t
 /test/gost2814789t
@@ -92,35 +48,32 @@ Makefile
 /test/ssltest_old
 /test/x509aux
 /test/v3ext
-*.so*
-*.dylib*
-*.dll*
-*.exe
-*.pyc
-*.exp
-*.lib
-*.pdb
-*.ilk
-*.def
-*.rc
-*.res
-# Exceptions
-!/test/bctest
-!/crypto/des/times/486-50.sol
+
+# Certain files that get created by tests on the fly
+/test/*.ss
+/test/*.srl
+/test/.rnd
+/test/test*.pem
+/test/newkey.pem
+/test/*.log
+/test/buildtest_*
+
+# Fuzz stuff.
+# Anything without an extension is an executable on Unix, so we keep files
+# with extensions.  And we keep the corpora subddir versioned as well.
+# Anything more generic with extensions that should be ignored will be taken
+# care of by general ignores for those extensions (*.o, *.obj, *.exe, ...)
+/fuzz/*
+!/fuzz/README*
+!/fuzz/corpora
+!/fuzz/*.*
 
 # Misc auto generated files
 /include/openssl/opensslconf.h
 /tools/c_rehash
 /tools/c_rehash.pl
-/crypto/**/lib
-/engines/**/lib
-/ssl/**/lib
-Makefile.save
-*.bak
 /tags
 /TAGS
-cscope.*
-*.d
 /crypto.map
 /ssl.map
 
@@ -168,3 +121,51 @@ cscope.*
 /test/fips_shatest.c
 /test/fips_test_suite.c
 /test/shatest.c
+
+##### Generic patterns
+# Auto generated assembly language source files
+*.s
+!/crypto/*/asm/*.s
+/crypto/arm*.S
+/crypto/*/*.S
+*.asm
+!/crypto/*/asm/*.asm
+
+# Object files
+*.o
+*.obj
+
+# editor artefacts
+*.swp
+.#*
+\#*#
+*~
+
+# Certificate symbolic links
+*.0
+
+# All kinds of executables
+*.so
+*.so.*
+*.dylib
+*.dylib.*
+*.dll
+*.dll.*
+*.exe
+*.pyc
+*.exp
+*.lib
+*.pdb
+*.ilk
+*.def
+*.rc
+*.res
+
+# Misc generated stuff
+Makefile.save
+/crypto/**/lib
+/engines/**/lib
+/ssl/**/lib
+*.bak
+cscope.*
+*.d