tests/tcg: Remove copy-pasted notes and from i386 and add x86_64 system tests to tests

The x86_64-softmmu Makefile seems to have been copy-pasted from the i386
Makefile at some point in the past. Cleaning up a vestigial unused
variable and removing some outdated comments.

Signed-off-by: Rowan Hart <rowanbhart@gmail.com>
Message-ID: <20250624175351.440780-7-rowanbhart@gmail.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-ID: <20250627112512.1880708-11-alex.bennee@linaro.org>

tests/tcg/x86_64/Makefile.softmmu-target

@@ -1,13 +1,11 @@
 #
-# x86 system tests
-#
-# This currently builds only for i386. The common C code is built
-# with standard compiler flags however so we can support both by
-# adding additional boot files for x86_64.
+# x86_64 system tests
 #
 
-I386_SYSTEM_SRC=$(SRC_PATH)/tests/tcg/i386/system
 X64_SYSTEM_SRC=$(SRC_PATH)/tests/tcg/x86_64/system
+X64_SYSTEM_TESTS=$(patsubst $(X64_SYSTEM_SRC)/%.c, %, $(wildcard $(X64_SYSTEM_SRC)/*.c))
+
+VPATH+=$(X64_SYSTEM_SRC)
 
 # These objects provide the basic boot code and helper functions for all tests
 CRT_OBJS=boot.o
@@ -18,7 +16,7 @@ LDFLAGS=-Wl,-T$(LINK_SCRIPT) -Wl,-melf_x86_64
 CFLAGS+=-nostdlib -ggdb -O0 $(MINILIB_INC)
 LDFLAGS+=-static -nostdlib $(CRT_OBJS) $(MINILIB_OBJS) -lgcc
 
-TESTS+=$(MULTIARCH_TESTS)
+TESTS+=$(MULTIARCH_TESTS) $(X64_SYSTEM_TESTS)
 EXTRA_RUNS+=$(MULTIARCH_RUNS)
 
 # building head blobs