Fix libdeflate.pc on Windows

Use Cflags.private to make the pkgconfig file specify the appropriate
flag when linking to libdeflate.dll on Windows.  To do this cleanly,
also invert the meaning of the flag, replacing LIBDEFLATE_DLL with
LIBDEFLATE_STATIC.  So now the DLL is the default, and LIBDEFLATE_STATIC
has to be defined when linking to the static library on Windows.

Fixes https://github.com/ebiggers/libdeflate/issues/229

Makefile

@@ -223,12 +223,13 @@ SHARED_LIB_OBJ := $(LIB_SRC:.c=.shlib.o)
 
 # Compile static library object files
 $(STATIC_LIB_OBJ): %.o: %.c $(LIB_HEADERS) $(COMMON_HEADERS) .build-config
-	$(QUIET_CC) $(CC) -o $@ -c $(CPPFLAGS) $(LIB_CFLAGS) $<
+	$(QUIET_CC) $(CC) -o $@ -c $(CPPFLAGS) $(LIB_CFLAGS) \
+		-DLIBDEFLATE_STATIC $<
 
 # Compile shared library object files
 $(SHARED_LIB_OBJ): %.shlib.o: %.c $(LIB_HEADERS) $(COMMON_HEADERS) .build-config
 	$(QUIET_CC) $(CC) -o $@ -c $(CPPFLAGS) $(LIB_CFLAGS) \
-		$(SHARED_LIB_CFLAGS) -DLIBDEFLATE_DLL $<
+		$(SHARED_LIB_CFLAGS) $<
 
 # Create static library
 $(STATIC_LIB):$(STATIC_LIB_OBJ)
@@ -263,6 +264,10 @@ PROG_CFLAGS += $(CFLAGS)		 \
 	       -D_FILE_OFFSET_BITS=64	 \
 	       -DHAVE_CONFIG_H
 
+ifndef USE_SHARED_LIB
+PROG_CFLAGS += -DLIBDEFLATE_STATIC
+endif
+
 ALL_PROG_COMMON_HEADERS := programs/config.h \
 			   programs/prog_util.h \
 			   programs/test_util.h

Makefile.msc

@@ -40,10 +40,10 @@ PROG_CFLAGS = $(CFLAGS) -Iprograms
 all: $(STATIC_LIB) $(SHARED_LIB) $(IMPORT_LIB) gzip.exe gunzip.exe
 
 .c.obj:
-	$(CC) -c /Fo$@ $(CFLAGS) $**
+	$(CC) -c /Fo$@ $(CFLAGS) /DLIBDEFLATE_STATIC $**
 
 .c.dllobj:
-	$(CC) -c /Fo$@ $(CFLAGS) /DLIBDEFLATE_DLL $**
+	$(CC) -c /Fo$@ $(CFLAGS) $**
 
 $(STATIC_LIB): $(STATIC_LIB_OBJ)
 	$(AR) $(ARFLAGS) -out:$@ $(STATIC_LIB_OBJ)

libdeflate.h

@@ -17,18 +17,20 @@ extern "C" {
 #include <stdint.h>
 
 /*
- * On Windows, if you want to link to the DLL version of libdeflate, then
- * #define LIBDEFLATE_DLL.  Note that the calling convention is "cdecl".
+ * On Windows, you must define LIBDEFLATE_STATIC if you are linking to the
+ * static library version of libdeflate instead of the DLL.  On other platforms,
+ * LIBDEFLATE_STATIC has no effect.
  */
-#ifdef LIBDEFLATE_DLL
-#  ifdef BUILDING_LIBDEFLATE
-#    define LIBDEFLATEEXPORT	LIBEXPORT
-#  elif defined(_WIN32) || defined(__CYGWIN__)
+#ifdef _WIN32
+#  if defined(LIBDEFLATE_STATIC)
+#    define LIBDEFLATEEXPORT
+#  elif defined(BUILDING_LIBDEFLATE)
+#    define LIBDEFLATEEXPORT	__declspec(dllexport)
+#  else
 #    define LIBDEFLATEEXPORT	__declspec(dllimport)
 #  endif
-#endif
-#ifndef LIBDEFLATEEXPORT
-#  define LIBDEFLATEEXPORT
+#else
+#  define LIBDEFLATEEXPORT	__attribute__((visibility("default")))
 #endif
 
 #if defined(BUILDING_LIBDEFLATE) && defined(__GNUC__) && defined(__i386__)

libdeflate.pc.in

@@ -3,3 +3,4 @@ Description: Fast implementation of DEFLATE, zlib, and gzip
 Version: @VERSION@
 Libs: -L@LIBDIR@ -ldeflate
 Cflags: -I@INCDIR@
+Cflags.private: -DLIBDEFLATE_STATIC