package/pkg-meson: improve generation of cross-compilation file

Removed a few variables, as they were only used to communicate
between the meson package and pkg-meson.mk and are not needed
anymore.

Moved cross-compilation.conf.in out of meson package.

Creating the cross-compilation.conf files for packages is now
using the original template.
To avoid duplicate code, the common sed pattern is stored in
a make variable.

Use explicit Buildroot variables for compiler tools,
and some fixes. (TARGET_LDFLAGS and TARGET_CXXFLAGS
were mixed up with PKG_TARGET_CFLAGS)

Signed-off-by: Norbert Lange <nolange79@gmail.com>
[Arnout: keep PKG_MESON_INSTALL_CROSS_CONF in
TOOLCHAIN_TARGET_FINALIZE_HOOKS]
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>

support/misc/cross-compilation.conf.in

@@ -0,0 +1,32 @@
+# Note: Buildroot's and Meson's terminologies differ about the meaning
+# of 'build', 'host' and 'target':
+# - Buildroot's 'host' is Meson's 'build'
+# - Buildroot's 'target' is Meson's 'host'
+
+[binaries]
+c = '@TARGET_CC@'
+cpp = '@TARGET_CXX@'
+ar = '@TARGET_AR@'
+strip = '@TARGET_STRIP@'
+pkgconfig = '@PKGCONF_HOST_BINARY@'
+g-ir-compiler = '@STAGING_DIR@/usr/bin/g-ir-compiler'
+g-ir-scanner = '@STAGING_DIR@/usr/bin/g-ir-scanner'
+
+[built-in options]
+c_args = [@TARGET_CFLAGS@]
+c_link_args = [@TARGET_LDFLAGS@]
+cpp_args = [@TARGET_CXXFLAGS@]
+cpp_link_args = [@TARGET_LDFLAGS@]
+wrap_mode = 'nodownload'
+
+[properties]
+needs_exe_wrapper = true
+sys_root = '@STAGING_DIR@'
+pkg_config_libdir = '@STAGING_DIR@/usr/lib/pkgconfig:@STAGING_DIR@/usr/share/pkgconfig'
+pkg_config_static = '@STATIC@'
+
+[host_machine]
+system = 'linux'
+cpu_family = '@TARGET_ARCH@'
+cpu = '@TARGET_CPU@'
+endian = '@TARGET_ENDIAN@'