test: add host-side unit-test harness, covering cmd_editor

Compile selected firmware translation units unmodified under host gcc with
AddressSanitizer and UBSan, force-including a shim header that erases the
SDCC 8051 keywords, and link them against a mocked serial ring and console.
A first suite covers the CLI line editor: line entry, backspace editing,
and both long-input overflow cases (length cap and ring-pointer stall).

The only firmware-source change is one #ifndef RTLP_HOST_TEST block in
rtl837x_common.h grouping the libc-named prototypes (sleep/memcpy/memset/
strlen/strcpy/strcmp) so host builds take them from the C library instead;
on-target builds are unaffected.

Run with: make -C test

rtl837x_common.h

@@ -158,7 +158,6 @@ void reg_write_m(uint16_t reg_addr);
 void sds_read(uint8_t sds_id, uint8_t page, uint8_t reg);
 void sds_write_v(uint8_t sds_id, uint8_t page, uint8_t reg, uint16_t v);
 void delay(uint16_t t);
-void sleep(uint16_t t);
 void write_char_no_syslog(char c);
 void write_char(char c);
 void print_reg(uint16_t reg);
@@ -170,15 +169,22 @@ uint8_t reg_bit_test(uint16_t reg_addr, char bit);
 void sfr_mask_data(uint8_t n, uint8_t mask, uint8_t set);
 void sfr_set_zero(void);
 void reset_chip(void);
+/* Firmware implementations that shadow libc names. Host unit-test builds
+ * (RTLP_HOST_TEST) hide these prototypes so they don't clash with glibc;
+ * argument order matches libc, so on-host callers transparently use the
+ * C library. See test/. */
+#ifndef RTLP_HOST_TEST
+void sleep(uint16_t t);
 void memcpy(__xdata void * __xdata dst, __xdata const void * __xdata src, uint16_t len);
-void memcpyc(__xdata uint8_t *dst, __code uint8_t *src, uint16_t len);
 void memset(__xdata uint8_t *dst, __xdata uint8_t v, uint8_t len);
 int memcmp(__xdata const void *a, __xdata const void *b, uint16_t len);
 uint16_t strlen(__code const char *s);
-uint16_t strlen_x(__xdata const char *s);
-uint16_t strtox(__xdata uint8_t *dst, __code const char *s);
 uint16_t strcpy(__xdata uint8_t *dst, const char *s);
 char strcmp(__xdata const uint8_t *a, __code const uint8_t *b);
+#endif
+void memcpyc(__xdata uint8_t *dst, __code uint8_t *src, uint16_t len);
+uint16_t strlen_x(__xdata const char *s);
+uint16_t strtox(__xdata uint8_t *dst, __code const char *s);
 bool strstart(__xdata const uint8_t *a, __code const uint8_t *b);
 bool strstart_x(__xdata const uint8_t *a, __xdata const uint8_t *b);
 void tcpip_output(void);