Install gawk in gcc container

Cannot even build hello world without gawk. also it is a POSIX standard
package.

src/bci_build/package/gcc.py

@@ -46,6 +46,7 @@ def _is_main_gcc(os_version: OsVersion, gcc_version: _GCC_VERSIONS) -> bool:
                 (gcc_pkg := f"gcc{gcc_version}"),
                 (gpp := f"{gcc_pkg}-c++"),
                 "make",
+                "gawk",
             ]
             + (["gcc", "gcc-c++"] if _is_main_gcc(os_version, gcc_version) else [])
         ),