lmdb: fix compilation with glibc

Signed-off-by: Rosen Penev <rosenp@gmail.com>

libs/lmdb/Makefile

@@ -2,7 +2,7 @@ include $(TOPDIR)/rules.mk
 
 PKG_NAME:=lmdb
 PKG_VERSION:=0.9.24
-PKG_RELEASE:=2
+PKG_RELEASE:=3
 
 PKG_SOURCE:=LMDB_$(PKG_VERSION).tar.gz
 PKG_SOURCE_URL:=https://codeload.github.com/LMDB/lmdb/tar.gz/LMDB_$(PKG_VERSION)?
@@ -64,7 +64,7 @@ define Build/Compile
 	$(MAKE) -C "$(PKG_BUILD_DIR)/$(MAKE_PATH)/" \
 		CC="$(TARGET_CC)" \
 		CFLAGS+="$(TARGET_CFLAGS)" \
-		LDFLAGS+="$(TARGET_LDFLAGS)" \
+		LDFLAGS+="$(TARGET_LDFLAGS) $(if $(CONFIG_USE_GLIBC),-lpthread)" \
 		FPIC="$(FPIC)" \
 		AR="$(TARGET_AR)"
 endef