Makefile.am: Avoid using subdir if arch is not required

There's no need in going a level deeper if we already know nothing's
going to be done. This way we also get cleaner make outputs.

Reference: https://www.gnu.org/software/automake/manual/html_node/Conditional-Subdirectories.html#Conditional-Subdirectories

Related: OS#3029

Change-Id: I3ff57ab14edc575904e8137929a0ef02c95e03af

Transceiver52M/Makefile.am

@@ -24,7 +24,11 @@ include $(top_srcdir)/Makefile.common
 AM_CPPFLAGS = -Wall $(STD_DEFINES_AND_INCLUDES) -I${srcdir}/common
 AM_CXXFLAGS = -lpthread $(LIBOSMOCORE_CFLAGS) $(LIBOSMOCTRL_CFLAGS) $(LIBOSMOVTY_CFLAGS)
 
-SUBDIRS = arm x86
+if ARCH_ARM
+SUBDIRS = arm
+else
+SUBDIRS = x86
+endif
 
 if USRP1
 AM_CPPFLAGS += $(USRP_CFLAGS)

Transceiver52M/arm/Makefile.am

@@ -1,4 +1,3 @@
-if ARCH_ARM
 if ARCH_ARM_A15
 ARCH_FLAGS = -mfpu=neon-vfpv4
 else
@@ -20,4 +19,3 @@ libarch_la_SOURCES = \
 	scale_neon.S \
 	mult.c \
 	mult_neon.S
-endif

Transceiver52M/x86/Makefile.am

@@ -1,4 +1,3 @@
-if !ARCH_ARM
 AM_CFLAGS = -Wall -std=gnu99 -I${srcdir}/../common
 
 noinst_LTLIBRARIES = libarch.la
@@ -29,4 +28,3 @@ libarch_la_SOURCES = \
 	../common/convert_base.c \
 	convert.c \
 	convolve.c
-endif