kconfig: port qconf to work with Qt6 in addition to Qt5

Tested with Qt5 5.15 and Qt6 6.4. Note that earlier versions of Qt5
are no longer guaranteed to work.

Signed-off-by: Boris Kolpackov <boris@codesynthesis.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

kconfig: refactor Makefile to reduce process forks

Refactor Makefile and use read-file macro. For Make >= 4.2, it can read
out a file by using the built-in function.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>

kconfig: Qt5: tell the user which packages are required

Along with saying "Please install Qt5 ...", tell exactly which
parts of Qt5 are needed. This is useful when parts of Qt5 are
installed but some of the required pieces are missing, and it
eliminates the need for the user to find the shell script and
the line in it that provide that information.

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

kbuild: Allow kernel installation packaging to override pkg-config

Add HOSTPKG_CONFIG to allow tooling that builds the kernel to override
what pkg-config and parameters are used.

Signed-off-by: Chun-Tse Shao <ctshao@google.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

kconfig: qconf: use a variable to pass packages to pkg-config

The variable, PKG, is defined at the beginning of this script.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

kconfig: qconf: drop Qt4 support

It is possible to keep this compatible with both Qt4 and Qt5, but it is
questionable if it is worth the efforts; it would require us to test
this on both of them, and prevent us from using new features in Qt5.

Qt5 was released in 2012, and now widely available.

Drop the Qt4 support.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

kconfig: do not require pkg-config on make {menu,n}config

Meelis Roos reported a {menu,n}config regression:
"I have libncurses devel package installed in the default system
location (as do 99%+ on actual developers probably) and in this
case, pkg-config is useless. pkg-config is needed only when
libraries and headers are installed in non-default locations but
it is bad to require installation of pkg-config on all the machines
where make menuconfig would be possibly run."

For {menu,n}config, do not use pkg-config if it is not installed.
For {g,x}config, keep checking pkg-config since we really rely on it
for finding the installation paths of the required packages.

Fixes: 4ab3b80159d4 ("kconfig: check for pkg-config on make {menu,n,g,x}config")
Reported-by: Meelis Roos <mroos@linux.ee>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Tested-by: Meelis Roos <mroos@linux.ee>
Tested-by: Randy Dunlap <rdunlap@infradead.org>

kconfig: refactor Qt package checks for building qconf

Currently, the necessary package checks for building qconf is
surrounded by ifeq ($(MAKECMDGOALS),xconfig) ... endif.
Then, Make will restart when .tmp_qtcheck is generated.

To simplify the Makefile, move the scripting to a separate file,
and use filechk. The shell script is executed everytime xconfig
is run, but it is not a costly script.

In the old code, 'pkg-config --exists' only checked Qt5Core / QtCore,
but the set of necessary packages should be checked.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Tested-by: Randy Dunlap <rdunlap@infradead.org>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>