package/zstd: fix build without threads

Move libzstd.pc in ZSTD_BUILD_LIBS so it will be suffixed by -nomt
without threads. As a result, libzstd.pc will not contain -pthread in
Libs.Private which will avoid the following static build failure with
zchunk) raised since commit 0f0e913f10caf21f23c2e46f210519a7a3bc0b32:

/home/buildroot/autobuild/instance-2/output-1/host/bin/aarch64_be-buildroot-linux-uclibc-gcc  -o src/unzck src/unzck.p/unzck.c.o src/unzck.p/util_common.c.o -Wl,--as-needed -Wl,--no-undefined -static -Wl,--start-group src/lib/libzck.a -largp /home/buildroot/autobuild/instance-2/output-1/host/aarch64_be-buildroot-linux-uclibc/sysroot/usr/lib/libzstd.a -pthread /home/buildroot/autobuild/instance-2/output-1/host/aarch64_be-buildroot-linux-uclibc/sysroot/usr/lib/libssl.a /home/buildroot/autobuild/instance-2/output-1/host/aarch64_be-buildroot-linux-uclibc/sysroot/usr/lib/libcrypto.a -Wl,--end-group
/home/buildroot/autobuild/instance-2/output-1/host/lib/gcc/aarch64_be-buildroot-linux-uclibc/10.3.0/../../../../aarch64_be-buildroot-linux-uclibc/bin/ld: cannot find -lpthread

Fixes:
 - http://autobuild.buildroot.org/results/481d1979920daaecac48dec763151e124651740f

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>

package/zstd/zstd.mk

@@ -38,14 +38,15 @@ endif
 # zstd will append -O3 after $(CFLAGS), use MOREFLAGS to override again
 ZSTD_OPTS += MOREFLAGS="$(TARGET_OPTIMIZATION)"
 
+ZSTD_BUILD_LIBS_BASENAMES = libzstd.pc
 ifeq ($(BR2_STATIC_LIBS),y)
-ZSTD_BUILD_LIBS = libzstd.a
+ZSTD_BUILD_LIBS_BASENAMES += libzstd.a
 ZSTD_INSTALL_LIBS = install-static
 else ifeq ($(BR2_SHARED_LIBS),y)
-ZSTD_BUILD_LIBS = lib
+ZSTD_BUILD_LIBS_BASENAMES += lib
 ZSTD_INSTALL_LIBS = install-shared
 else
-ZSTD_BUILD_LIBS = lib
+ZSTD_BUILD_LIBS_BASENAMES += lib
 ZSTD_INSTALL_LIBS = install-static install-shared
 endif
 
@@ -63,17 +64,20 @@ endif
 # purpose.
 ifeq ($(BR2_TOOLCHAIN_HAS_THREADS),y)
 ZSTD_OPTS += HAVE_THREAD=1
-ZSTD_BUILD_LIBS := $(addsuffix -mt,$(ZSTD_BUILD_LIBS))
+ZSTD_BUILD_LIBS_THREAD_SUFFIX = -mt
 else
 ZSTD_OPTS += HAVE_THREAD=0
-ZSTD_BUILD_LIBS := $(addsuffix -nomt,$(ZSTD_BUILD_LIBS))
+ZSTD_BUILD_LIBS_THREAD_SUFFIX = -nomt
 endif
 # check-package disable OverriddenVariable - override intended
-ZSTD_BUILD_LIBS := $(addsuffix -release,$(ZSTD_BUILD_LIBS))
+ZSTD_BUILD_LIBS = \
+	$(addsuffix -release, \
+		$(addsuffix $(ZSTD_BUILD_LIBS_THREAD_SUFFIX), \
+			$(ZSTD_BUILD_LIBS_BASENAMES)))
 
 define ZSTD_BUILD_CMDS
 	$(TARGET_MAKE_ENV) $(TARGET_CONFIGURE_OPTS) $(MAKE) $(ZSTD_OPTS) \
-		-C $(@D)/lib $(ZSTD_BUILD_LIBS) libzstd.pc
+		-C $(@D)/lib $(ZSTD_BUILD_LIBS)
 	$(TARGET_MAKE_ENV) $(TARGET_CONFIGURE_OPTS) $(MAKE) $(ZSTD_OPTS) \
 		-C $(@D)/programs $(ZSTD_BUILD_PROG_TARGET)
 endef