[build] Add support for ASM files in Make + CMake

* Extract out common portion of `lib/Makefile` into `lib/libzstd.mk`.
  Most relevantly, the way we find library files.
* Use `lib/libzstd.mk` in the other Makefiles instead of repeating the
  same code.
* Add a test `tests/test-variants.sh` that checks that the builds of
  `make -C programs allVariants` are correct, and run it in Actions.
* Adds support for ASM files in the CMake build.

The Meson build is not updated because it lists every file in zstd,
and supports ASM off the bat, so the Huffman ASM commit will just add
the ASM file to the list.

The Visual Studios build is not updated because I'm not adding ASM
support to Visual Studios yet.

tests/fuzz/Makefile

@@ -23,6 +23,12 @@ else
 endif
 CORPORA_URL_PREFIX:=https://github.com/facebook/zstd/releases/download/fuzz-corpora/
 
+LIBZSTD = ../../lib
+DEBUGLEVEL ?= 2
+ZSTD_LEGACY_SUPPORT ?= 1
+
+include $(LIBZSTD)/libzstd.mk
+
 ZSTDDIR = ../../lib
 PRGDIR = ../../programs
 CONTRIBDIR = ../../contrib
@@ -34,7 +40,7 @@ FUZZ_EXTRA_FLAGS := -Wall -Wextra -Wcast-qual -Wcast-align -Wshadow \
 	-Wstrict-aliasing=1 -Wswitch-enum -Wdeclaration-after-statement \
 	-Wstrict-prototypes -Wundef \
 	-Wvla -Wformat=2 -Winit-self -Wfloat-equal -Wwrite-strings \
-	-Wredundant-decls \
+	-Wredundant-decls -Wno-deprecated-declarations \
 	-g -fno-omit-frame-pointer
 FUZZ_CFLAGS := $(FUZZ_EXTRA_FLAGS) $(CFLAGS)
 FUZZ_CXXFLAGS := $(FUZZ_EXTRA_FLAGS) -std=c++11 $(CXXFLAGS)
@@ -50,11 +56,11 @@ FUZZ_SRC := $(PRGDIR)/util.c ./fuzz_helpers.c ./zstd_helpers.c ./fuzz_data_produ
 SEEKABLE_HEADERS = $(CONTRIBDIR)/seekable_format/zstd_seekable.h
 SEEKABLE_OBJS = $(CONTRIBDIR)/seekable_format/zstdseek_compress.c $(CONTRIBDIR)/seekable_format/zstdseek_decompress.c
 
-ZSTDCOMMON_SRC := $(ZSTDDIR)/common/*.c
-ZSTDCOMP_SRC   := $(ZSTDDIR)/compress/*.c
-ZSTDDECOMP_SRC := $(ZSTDDIR)/decompress/*.c
-ZSTDDICT_SRC := $(ZSTDDIR)/dictBuilder/*.c
-ZSTDLEGACY_SRC := $(ZSTDDIR)/legacy/*.c
+ZSTDCOMMON_SRC := $(ZSTD_COMMON_FILES)
+ZSTDCOMP_SRC   := $(ZSTD_COMPRESS_FILES)
+ZSTDDECOMP_SRC := $(ZSTD_DECOMPRESS_FILES)
+ZSTDDICT_SRC := $(ZSTD_DICTBUILDER_FILES)
+ZSTDLEGACY_SRC := $(ZSTD_LEGACY_FILES)
 FUZZ_SRC       := \
 	$(FUZZ_SRC) \
 	$(ZSTDDECOMP_SRC) \
@@ -71,7 +77,8 @@ FUZZ_D_OBJ4 := $(subst $(ZSTDDIR)/dictBuilder/,d_lib_dictBuilder_,$(FUZZ_D_OBJ3)
 FUZZ_D_OBJ5 := $(subst $(ZSTDDIR)/legacy/,d_lib_legacy_,$(FUZZ_D_OBJ4))
 FUZZ_D_OBJ6 := $(subst $(PRGDIR)/,d_prg_,$(FUZZ_D_OBJ5))
 FUZZ_D_OBJ7 := $(subst $\./,d_fuzz_,$(FUZZ_D_OBJ6))
-FUZZ_DECOMPRESS_OBJ := $(FUZZ_D_OBJ7:.c=.o)
+FUZZ_D_OBJ8 := $(FUZZ_D_OBJ7:.c=.o)
+FUZZ_DECOMPRESS_OBJ := $(FUZZ_D_OBJ8:.S=.o)
 
 FUZZ_RT_OBJ1 := $(subst $(ZSTDDIR)/common/,rt_lib_common_,$(FUZZ_SRC))
 FUZZ_RT_OBJ2 := $(subst $(ZSTDDIR)/compress/,rt_lib_compress_,$(FUZZ_RT_OBJ1))
@@ -80,7 +87,8 @@ FUZZ_RT_OBJ4 := $(subst $(ZSTDDIR)/dictBuilder/,rt_lib_dictBuilder_,$(FUZZ_RT_OB
 FUZZ_RT_OBJ5 := $(subst $(ZSTDDIR)/legacy/,rt_lib_legacy_,$(FUZZ_RT_OBJ4))
 FUZZ_RT_OBJ6 := $(subst $(PRGDIR)/,rt_prg_,$(FUZZ_RT_OBJ5))
 FUZZ_RT_OBJ7 := $(subst $\./,rt_fuzz_,$(FUZZ_RT_OBJ6))
-FUZZ_ROUND_TRIP_OBJ := $(FUZZ_RT_OBJ7:.c=.o)
+FUZZ_RT_OBJ8 := $(FUZZ_RT_OBJ7:.c=.o)
+FUZZ_ROUND_TRIP_OBJ := $(FUZZ_RT_OBJ8:.S=.o)
 
 .PHONY: default all clean cleanall
 
@@ -117,6 +125,9 @@ rt_lib_compress_%.o: $(ZSTDDIR)/compress/%.c
 rt_lib_decompress_%.o: $(ZSTDDIR)/decompress/%.c
 	$(CC) $(FUZZ_CPPFLAGS) $(FUZZ_CFLAGS) $(FUZZ_ROUND_TRIP_FLAGS) $< -c -o $@
 
+rt_lib_decompress_%.o: $(ZSTDDIR)/decompress/%.S
+	$(CC) $(FUZZ_CPPFLAGS) $(FUZZ_CFLAGS) $(FUZZ_ROUND_TRIP_FLAGS) $< -c -o $@
+
 rt_lib_dictBuilder_%.o: $(ZSTDDIR)/dictBuilder/%.c
 	$(CC) $(FUZZ_CPPFLAGS) $(FUZZ_CFLAGS) $(FUZZ_ROUND_TRIP_FLAGS) $< -c -o $@
 
@@ -138,6 +149,9 @@ d_lib_compress_%.o: $(ZSTDDIR)/compress/%.c
 d_lib_decompress_%.o: $(ZSTDDIR)/decompress/%.c
 	$(CC) $(FUZZ_CPPFLAGS) $(FUZZ_CFLAGS) $< -c -o $@
 
+d_lib_decompress_%.o: $(ZSTDDIR)/decompress/%.S
+	$(CC) $(FUZZ_CPPFLAGS) $(FUZZ_CFLAGS) $< -c -o $@
+
 d_lib_dictBuilder_%.o: $(ZSTDDIR)/dictBuilder/%.c
 	$(CC) $(FUZZ_CPPFLAGS) $(FUZZ_CFLAGS) $< -c -o $@