libcap: clean up configuration variables

There's no need to set PACKAGECONFIG:class-native as we disable PAM in
the native DISTRO_FEATURES.

No need to set COPTS, since "Canonicalize build system"[1] the exported
CFLAGS/CPPFLAGS/LDFLAGS are respected.

Merge multiple make arguments into EXTRA_OEMAKE to remove duplication.

SYSTEM_HEADERS is not used upstream, remove.

[1] 2762c2c1a8c98d9012fcd40f20d133493a0b3219

(From OE-Core rev: 88cd79eee6dcc40d0e75ab35d9092ac3c788be7d)

Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/recipes-support/libcap/libcap_2.74.bb

@@ -23,11 +23,10 @@ UPSTREAM_CHECK_URI = "https://www.kernel.org/pub/linux/libs/security/linux-privs
 inherit lib_package
 
 PACKAGECONFIG ??= "${@bb.utils.filter('DISTRO_FEATURES', 'pam', d)}"
-PACKAGECONFIG:class-native ??= ""
-
 PACKAGECONFIG[pam] = "PAM_CAP=yes,PAM_CAP=no,libpam"
 
 EXTRA_OEMAKE = " \
+  ${PACKAGECONFIG_CONFARGS} \
   INDENT=  \
   lib='${baselib}' \
   RAISE_SETFCAP=no \
@@ -35,23 +34,16 @@ EXTRA_OEMAKE = " \
   USE_GPERF=yes \
 "
 
-EXTRA_OEMAKE:append:class-target = " SYSTEM_HEADERS=${STAGING_INCDIR}"
-
 do_compile() {
-	unset CFLAGS BUILD_CFLAGS
 	oe_runmake \
-		${PACKAGECONFIG_CONFARGS} \
 		AR="${AR}" \
 		CC="${CC}" \
 		RANLIB="${RANLIB}" \
-                OBJCOPY="${OBJCOPY}" \
+		OBJCOPY="${OBJCOPY}"
-		COPTS="${CFLAGS}" \
-		BUILD_COPTS="${BUILD_CFLAGS}"
 }
 
 do_install() {
 	oe_runmake install \
-		${PACKAGECONFIG_CONFARGS} \
 		DESTDIR="${D}" \
 		prefix="${prefix}" \
 		SBINDIR="${sbindir}"