How can I resolve clang input unused in multiple indirection Makefile?

Question

I'm trying to write a makefile that will enable a test suite runner, test.c, to run. However, I think my use of the -c flag is getting in the way.

all: parser

parser_out.o: parser_out.h parser_out.c
    clang -c -g parser_out.c
    
parser_loader.o: parser_loader.h parser_loader.c parser_mem.o
    clang -c -g lc4_mem.o parser_loader.c
    
parser_mem.o: parser_mem.h parser_mem.c
    clang -c -g parser_mem.c

parser: parser.c parser_mem.o parser_loader.o parser_out.o
    clang parser.c -g parser_mem.o parser_loader.o parser_out.o -o parser

tests: test

test_helpers.o: test_helpers.c test_helpers.h
    clang test_helpers.c -c -g

parser_loader.test.o: parser_loader.test.h parser_loader.test.c parser_loader.o test_helpers.o
    clang parser_loader.test.c -g parser_loader.o test_helpers.o

test: test.c parser_loader.test.o
    clang test.c -g parser_loader.test.o -o test

make all works as expected.

make tests fails and indicates that references to methods in parser_mem.c are undefined.

make parser_loader.test.o results in the same error as make tests.

If I include parser_mem.o directly in the linking of parser_loader.test.o, the errors caused by linking to my files disappear. But, an error indicating invalid linking to GNU remains:

/usr/bin/../lib/gcc/x86_64-linux-gnu/7.5.0/../../../x86_64-linux-gnu/crt1.o: In function `_start':
(.text+0x20): undefined reference to `main'

1. Why aren't my references through references being handled successfully?
2. Why is clang suddenly struggling to compile with system links?