Ignore PKG_CONFIG* shell exports for Yocto

Yocto sets GN_HOST_PKG_CONFIG script for native
tools builds, therefore skip host pkg-config script
generation even if PKG_CONFIG* shell variables for target
are exported.

Task-number: QTBUG-66275
Change-Id: I4a9939cd67ca5f32faeb827b5df0d3274ae7c30e
Reviewed-by: Samuli Piippo <samuli.piippo@qt.io>

src/core/config/linux.pri

@@ -115,12 +115,12 @@ host_build {
         PKG_CONFIG_HOST = $$(GN_PKG_CONFIG_HOST)
         pkgConfigLibDir = $$(PKG_CONFIG_LIBDIR)
         pkgConfigSysrootDir = $$(PKG_CONFIG_SYSROOT_DIR)
-        isEmpty(PKG_CONFIG_HOST): PKG_CONFIG_HOST = $$QMAKE_PKG_CONFIG_HOST
-        cross_compile {
+        isEmpty(PKG_CONFIG_HOST): cross_compile {
             !isEmpty(pkgConfigLibDir)|!isEmpty(pkgConfigSysrootDir) {
                 PKG_CONFIG_HOST = $$pkgConfigHostExecutable()
             }
         }
+        isEmpty(PKG_CONFIG_HOST): PKG_CONFIG_HOST = $$QMAKE_PKG_CONFIG_HOST
         gn_args += host_pkg_config=\"$$PKG_CONFIG_HOST\"
     }