[multi-asic] Fixed systemd-sonic-generator for multi-asic (#7954)

Why I did it

systemd-sonic-generator limits multi-asic unit file instances to 10 (single digit instance number 0 - 10). This limitation needs to be removed to handle more than 10 asics.
MAX_NUM_TARGETS and MAX_NUM_INSTALL_LINES limits to 15 which is not sufficient for systems with more than 15 asics.
Inside get_unit_files(), strcmp produce incorrect results due to non null terminated string being compared.

 Added build UT support for systemd-sonic-generator

src/systemd-sonic-generator/.gitignore

@@ -1,4 +1,5 @@
 systemd-sonic-generator
+ssg_test
 debian/*
 !debian/changelog
 !debian/compat

src/systemd-sonic-generator/Makefile

@@ -1,5 +1,9 @@
 CC=gcc
-CFLAGS=-std=gnu99
+CFLAGS=-std=gnu99 -D_GNU_SOURCE
+
+CPP=g++
+CPPFLAGS=-std=c++11 -D_GNU_SOURCE
+LFLAGS=-lpthread -lboost_filesystem -lboost_system -lgtest
 
 BINARY = systemd-sonic-generator
 MAIN_TARGET = $(BINARY)_1.0.0_$(CONFIGURED_ARCH).deb
@@ -20,3 +24,18 @@ install: $(BINARY)
 	mkdir -p $(DESTDIR)/lib/systemd
 	mkdir -p $(DESTDIR)/lib/systemd/system-generators
 	cp ./systemd-sonic-generator $(DESTDIR)/lib/systemd/system-generators
+
+.PHONY: test
+test: ssg_test
+	./ssg_test
+
+ssg_test: ssg-test.cc systemd-sonic-generator.o
+	$(CPP) $(CPPFLAGS) -o $@ $^ $(LFLAGS)
+
+systemd-sonic-generator.o: systemd-sonic-generator.c
+	$(CC) $(CFLAGS) -D_SSG_UNITTEST -o $@ -c $^
+
+clean:
+	rm -f ./systemd-sonic-generator
+	rm -f ./systemd-sonic-generator.o
+	rm -f ./ssg_test

src/systemd-sonic-generator/debian/rules

@@ -8,7 +8,6 @@ PACKAGEVERSION = $(VERSION)
 	dh $@
 
 override_dh_auto_clean:
-override_dh_auto_test:
 override_dh_auto_build:
 override_dh_auto_install:
 	make systemd-sonic-generator