unit-tests: link common compare helper

Add src/string.c to TPM unit targets that compile tpm.c inline so wolfBoot_constant_compare resolves after its move out of TPM-only code.

F/CI

Author: danielinux

tools/unit-tests/Makefile

@@ -148,13 +148,13 @@ unit-spi-flash: ../../include/target.h unit-spi-flash.c
 unit-qspi-flash: ../../include/target.h unit-qspi-flash.c
 	gcc -o $@ $^ $(CFLAGS) $(LDFLAGS)
 
-unit-tpm-rsa-exp: ../../include/target.h unit-tpm-rsa-exp.c
+unit-tpm-rsa-exp: ../../include/target.h unit-tpm-rsa-exp.c ../../src/string.c
 	gcc -o $@ $^ $(CFLAGS) -I$(WOLFBOOT_LIB_WOLFTPM) -DWOLFBOOT_TPM \
 		-DWOLFTPM_USER_SETTINGS -DWOLFBOOT_TPM_VERIFY -DWOLFBOOT_SIGN_RSA2048 \
 		-DWOLFBOOT_HASH_SHA256 \
 		-ffunction-sections -fdata-sections $(LDFLAGS) -Wl,--gc-sections
 
-unit-tpm-check-rot-auth: ../../include/target.h unit-tpm-check-rot-auth.c
+unit-tpm-check-rot-auth: ../../include/target.h unit-tpm-check-rot-auth.c ../../src/string.c
 	gcc -o $@ $^ $(CFLAGS) -I$(WOLFBOOT_LIB_WOLFTPM) -DWOLFBOOT_TPM \
 		-DWOLFTPM_USER_SETTINGS -DWOLFBOOT_TPM_VERIFY -DWOLFBOOT_SIGN_RSA2048 \
 		-DWOLFBOOT_HASH_SHA256 \