replace some ifeq with prettier ifdef

Originally committed as revision 12764 to svn://svn.ffmpeg.org/ffmpeg/trunk

common.mak

@@ -4,7 +4,7 @@
 
 all: # make "all" default target
 
-ifeq ($(SUBDIR),)
+ifndef SUBDIR
 vpath %.c $(SRC_DIR)
 vpath %.h $(SRC_DIR)
 vpath %.S $(SRC_DIR)

libavcodec/Makefile

@@ -362,12 +362,12 @@ OBJS-$(HAVE_W32THREADS)                += w32thread.o
 
 OBJS-$(HAVE_XVMC)                      += xvmcvideo.o
 
-ifneq ($(CONFIG_SWSCALE),yes)
+ifndef CONFIG_SWSCALE
 OBJS += imgresample.o
 endif
 
 # processor-specific code
-ifeq ($(HAVE_MMX),yes)
+ifdef HAVE_MMX
 OBJS += i386/fdct_mmx.o \
         i386/cputest.o \
         i386/dsputil_mmx.o \

subdir.mak

@@ -19,7 +19,7 @@ endif
 INCINSTDIR := $(INCDIR)/lib$(NAME)
 
 define RULES
-ifeq ($(BUILD_SHARED),yes)
+ifdef BUILD_SHARED
 all: $(SUBDIR)$(SLIBNAME)
 
 install-libs: install-lib$(NAME)-shared
@@ -32,7 +32,7 @@ $(SUBDIR)$(SLIBNAME_WITH_MAJOR): $(OBJS)
 	$(CC) $(SHFLAGS) $(FFLDFLAGS) -o $$@ $$^ $(FFEXTRALIBS) $(EXTRAOBJS)
 	$(SLIB_EXTRA_CMD)
 
-ifneq ($(SUBDIR),)
+ifdef SUBDIR
 $(SUBDIR)$(SLIBNAME_WITH_MAJOR): \
     $(foreach L,$(FFLIBS),lib$(L)/$(SLIBPREF)$(L)$(SLIBSUF))
 endif