build: remove lib/.gitignore

This isn't required - we already have the whole build/
directory in the top level .gitignore.

When we remove build/lib/.gitignore, it means
build/lib directory must be created somewhere
before we try to place a library there. Top-level
builds get this directory created automatically,
but building directly from a sub-directory's
Makefile means we need to explicitly create
build/lib.  So add a mkdir -p to the LIB_C
macro to do exactly that to cover these cases.

Also simplify 'make clean' at the top level Makefile.
A lot of work went in there to work around this
.gitignore file that's not needed now that we've
fixed the underlying problem by getting rid of
it.

Suggested-by: John Levon <john.levon@nutanix.com>
Signed-off-by: Jim Harris <james.r.harris@intel.com>
Change-Id: Ibb92ff84d8c2a9bbe3e193c84f15ef3866f07b1f
Reviewed-on: https://review.spdk.io/gerrit/c/spdk/spdk/+/9169
Reviewed-by: Nick Connolly <nick.connolly@mayadata.io>
Reviewed-by: Aleksey Marchuk <alexeymar@mellanox.com>
Reviewed-by: Changpeng Liu <changpeng.liu@intel.com>
Reviewed-by: Tomasz Zawadzki <tomasz.zawadzki@intel.com>
Community-CI: Broadcom CI <spdk-ci.pdl@broadcom.com>
Community-CI: Mellanox Build Bot
Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>

Makefile

@@ -97,12 +97,7 @@ endif
 all: mk/cc.mk $(DIRS-y)
 clean: $(DIRS-y)
 	$(Q)rm -f include/spdk/config.h
-	$(Q)rm -rf build/bin
-	$(Q)rm -rf build/fio
-	$(Q)rm -rf build/examples
-	$(Q)rm -rf build/include
-	$(Q)rm -rf build/lib/pkgconfig
-	$(Q)find build/lib ! -name .gitignore -type f -delete
+	$(Q)rm -rf build
 
 install: all
 	$(Q)echo "Installed to $(DESTDIR)$(CONFIG_PREFIX)"

build/lib/.gitignore

@@ -1 +0,0 @@
-# Placeholder

mk/spdk.common.mk

@@ -358,6 +358,7 @@ BUILD_LINKERNAME_LIB=\
 LIB_C=\
 	$(Q)echo "  LIB $(notdir $@)"; \
 	rm -f $@; \
+	mkdir -p $(dir $@); \
 	$(CCAR) crDs $@ $(OBJS)
 
 # Clean up generated files listed as arguments plus a default list