Add 'corebinutils/csh/' from commit '9fcd5aad4bbd6e9e4e0791b193168db0bd861cb9'

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+# csh
+
+Standalone musl-libc-based Linux port of FreeBSD `csh` for Project Tick BSD/Linux Distribution.
+
+## Build
+
+```sh
+gmake -f GNUmakefile
+gmake -f GNUmakefile CC=musl-gcc
+```
+
+Binary output:
+
+```sh
+out/csh
+```
+
+## Test
+
+```sh
+gmake -f GNUmakefile test
+gmake -f GNUmakefile test CC=musl-gcc
+```
+
+## Port Strategy
+
+- The source base stays close to FreeBSD's `tcsh`, but the Linux build is standalone and generates its own `tc.defs.c`, `sh.err.h`, `ed.defns.h`, and `tc.const.h`.
+- The required upstream `tcsh` sources now live under `bin/csh/tcsh`, and the Linux terminfo/termcap stack is built from vendored ncurses sources under `bin/csh/ncurses`.
+- No shared BSD compatibility shim is introduced. FreeBSD-specific assumptions are replaced with Linux-native interfaces in the affected source files.
+- Child process accounting on Linux uses `wait4(2)` instead of BSD `wait3(2)`, which keeps job-control resource accounting working on musl.
+- Login/watch state reads Linux utmp/utmpx data from `_PATH_UTMP` when available, otherwise `/run/utmp`, rather than FreeBSD's `utx.active`.
+- Terminal capability lookup is satisfied by the vendored `libtinfow` build, so Linux and musl builds do not depend on host `ncursesw`/`tinfo`.
+- NLS catalogs are disabled in the standalone port at source level; the build does not install or load translated message catalogs.
+
+## Supported / Unsupported Linux Semantics
+
+- Supported: non-interactive `-c` execution, shell scripts, globbing, history-less `-f` operation, vendored termcap/terminfo lookups, job control/resource accounting via `wait4(2)`, `setpriority(2)`, `getrlimit(2)`, and `setrlimit(2)`.
+- Supported with explicit runtime dependency: login watch uses the host's utmp/utmpx database; if the database is absent, tcsh reports the missing file instead of silently pretending the feature works.
+- Unsupported in this standalone port: NLS catalog loading is disabled, so translated message catalogs are not installed or loaded.