Makefile: limit build targets for non-s390x architecture

A subset of s390 tools can be useful on non-s390x architectures such as
x86 or arm. Limit the build targets for these architectures with
'pvattest' and 'libpv' as the first candidates.

A cross compilation on x86 for s390x will still build the entire package
provided that the HOST_ARCH variable is set properly:

$ make HOST_ARCH=s390x CROSS_COMPILE=s390x-linux-gnu-

Cross compilation on s390x for x86 will limit the build targets as
described:

$ make HOST_ARCH=x86_64 CROSS_COMPILE=x86_64-linux-gnu-

Co-developed-by: Jan Höppner <hoeppner@linux.ibm.com>
Reviewed-by: Steffen Eiden <seiden@linux.ibm.com>
Signed-off-by: Marc Hartmayer <mhartmay@linux.ibm.com>
Signed-off-by: Steffen Eiden <seiden@linux.ibm.com>

CHANGELOG.md

@@ -22,6 +22,7 @@ Release history for s390-tools (MIT version)
     `CC_FOR_BUILD`. This is useful for cross compiling, and this naming
     convention is very similar to the Meson convention (see
     https://mesonbuild.com/Reference-tables.html#environment-variables-per-machine).
+  - add support for architectures other than s390x for `pvattest`
 
   Bug Fixes:
 

Makefile

@@ -6,6 +6,7 @@ include common.mak
 # LIBS: Libraries that can have a dependency to base libraries
 # TOOLS: Tools that can have a dependency to base libraries or libraries
 #
+ifeq ($(HOST_ARCH),s390x)
 BASELIB_DIRS = libutil libseckey
 LIB_DIRS = libvtoc libzds libdasd libccw libvmcp libekmfweb \
 	   libkmipclient libcpumf libap libpv
@@ -15,6 +16,11 @@ TOOL_DIRS = zipl zdump fdasd dasdfmt dasdview tunedasd \
 	   ziomon iucvterm hyptop cmsfs-fuse qethqoat zfcpdump zdsfs cpumf \
 	   systemd hmcdrvfs cpacfstats zdev dump2tar zkey netboot etc zpcictl \
 	   genprotimg lsstp hsci hsavmcore chreipl-fcp-mpath ap_tools pvattest
+else
+BASELIB_DIRS =
+LIB_DIRS = libpv
+TOOL_DIRS = pvattest
+endif
 
 SUB_DIRS = $(BASELIB_DIRS) $(LIB_DIRS) $(TOOL_DIRS)