tests2: keep linker boundary fixtures common

Compile _etext and _edata with -fcommon so RISC-V GCC does not
place them in .sbss. This preserves the intended common/BSS replacement
coverage.

Fixes the reported test-riscv64-linux failure:
https://github.com/TinyCC/tinycc/actions/runs/30347315549/job/90236450313

Author: idrassi

tests/tests2/Makefile

@@ -165,7 +165,7 @@ endif
 # Boundary symbols must cover separately named sections from external objects.
 150_linker_boundaries.test: NORUN = true
 150_linker_boundaries.test: T1 = ( \
-	$(CC) -fno-pic -fno-pie -c $(subst 150,150+,$1) \
+	$(CC) -fcommon -fno-pic -fno-pie -c $(subst 150,150+,$1) \
 		-o 150_linker_boundaries.o && \
 	$(TCC) $1 150_linker_boundaries.o -o $(basename $@).exe && \
 	./$(basename $@).exe \