gitignore: cleanups #2

A few more cleanups for .gitignore file.
The final goal is to have only files in there which
are generated during build.  Things like .orig or
.gdbinit are definitely not generated during build.
Also, anchor a few more build-time directories.
Signed-off-by: NMichael Tokarev <mjt@tls.msk.ru>

.gitignore

@@ -18,8 +18,8 @@
 /*-darwin-user
 /*-linux-user
 /*-bsd-user
-libdis*
-libuser
+/libdis*
+/libuser
 /linux-headers/asm
 /qga/qapi-generated
 /qapi-generated
@@ -52,7 +52,6 @@ libuser
 /fsdev/virtfs-proxy-helper
 /fsdev/virtfs-proxy-helper.1
 /fsdev/virtfs-proxy-helper.pod
-/.gdbinit
 *.a
 *.aux
 *.cp
@@ -81,12 +80,8 @@ libuser
 *.pc
 .libs
 .sdk
-*.swp
-*.orig
-.pc
 *.gcda
 *.gcno
-patches
 /pc-bios/bios-pq/status
 /pc-bios/vgabios-pq/status
 /pc-bios/optionrom/linuxboot.asm