.gitignore: add multiple items to .gitignore

Add /.vscode/, .clang-format and .gdb_history to .gitignore because:

 - For VSCode, workspace settings as well as debugging and task
 configurations are stored at the root in a .vscode folder;
 - For ClangFormat, the .clang-format file is searched relative to
 the current working directory when reading stdin;
 - For GDB, GDB command history file defaults to the value of the
 environment variable GDBHISTFILE, or to ./.gdb_history if this
 variable is not set.

Signed-off-by: Wang, Lei <lei4.wang@intel.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-Id: <20221020171921.1078533-1-lei4.wang@intel.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>

.gitignore

 /GNUmakefile
 /build/
 /.cache/
+/.vscode/
 *.pyc
 .sdk
 .stgit-*
 .git-submodule-status
+.clang-format
+.gdb_history
 cscope.*
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