package/meson: fix shared build issue due to --static flag always passed to pkg-config

Since cf75d7da98 we have a build failures when
building libgbm.so when valgrind package is selected because --static is always
passed to pkg-config even for shared build.

Even if -Dvalgrind=false on meson command line to build mesa, the valgrind
libraries come from pkg-config libdrm...

output/host/bin/pkg-config libdrm --libs --static
-L[...]/sysroot/usr/lib -ldrm -lm -L[...]/sysroot/usr/lib/valgrind
-lcoregrind-arm64-linux -lvex-arm64-linux -lgcc

... and break the build.

See initial discussions:
http://lists.busybox.net/pipermail/buildroot/2020-June/284543.html

This is due to a wrong condition test added by the patch
0004-mesonbuild-dependencies-base.py-add-pkg_config_stati.patch.

Indeed, pkg_config_static is a string, not a boolean; it is set to
either 'true' or 'aflse' by our meson package infra. Since the returned
object is a string, do not pass a boolean, but pas None (we only want to
test against the 'true' string, so we don't care what we get back when
it is not set, which never happens in Buildroot).

Before this patch, the issue can be reproduced using the following defconfig:
    BR2_aarch64=y
    BR2_TOOLCHAIN_EXTERNAL=y
    BR2_PACKAGE_VALGRIND=y
    BR2_PACKAGE_MESA3D=y
    BR2_PACKAGE_MESA3D_DRI_DRIVER_SWRAST=y

Fixes:
http://autobuild.buildroot.net/results/1b5/1b58d73ecbbe1af2c3e140563d696cf32d1c4a5a/build-end.log

Signed-off-by: Romain Naour <romain.naour@gmail.com>
Cc: James Hilliard <james.hilliard1@gmail.com>
Cc: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Cc: Fabrice Fontaine <fontaine.fabrice@gmail.com>
[yann.morin.1998@free.fr: slightly reword the commit log]
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>

package/meson/0004-mesonbuild-dependencies-base.py-add-pkg_config_stati.patch

@@ -1,4 +1,4 @@
-From 3a4962ede0d12bac66b38e0843f6e2ea75b03d50 Mon Sep 17 00:00:00 2001
+From 71295eec724f89ef5f5822c17cf44480335225cd Mon Sep 17 00:00:00 2001
 From: Fabrice Fontaine <fontaine.fabrice@gmail.com>
 Date: Sat, 15 Feb 2020 15:13:59 +0100
 Subject: [PATCH] mesonbuild/dependencies/base.py: add pkg_config_static
@@ -16,23 +16,26 @@ Fixes:
  - http://autobuild.buildroot.org/results/0d36952def63cb69628697fa6408aeb6ce10cb5b
 
 Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
+[Romain: Fix if condition, pkg_config_static is a string not a boolean]
+Signed-off-by: Romain Naour <romain.naour@gmail.com>
 ---
- mesonbuild/dependencies/base.py | 2 +-
- 1 file changed, 1 insertion(+), 1 deletion(-)
+ mesonbuild/dependencies/base.py | 3 ++-
+ 1 file changed, 2 insertions(+), 1 deletion(-)
 
 diff --git a/mesonbuild/dependencies/base.py b/mesonbuild/dependencies/base.py
-index a83e3d6c..913bff6b 100644
+index 5636602e..de4e87bc 100644
 --- a/mesonbuild/dependencies/base.py
 +++ b/mesonbuild/dependencies/base.py
-@@ -840,7 +840,7 @@ class PkgConfigDependency(ExternalDependency):
+@@ -858,7 +858,8 @@ class PkgConfigDependency(ExternalDependency):
      def _set_libs(self):
          env = None
          libcmd = [self.name, '--libs']
 -        if self.static:
-+        if self.static or self.env.properties[self.for_machine].get('pkg_config_static', False):
++        if self.static or \
++           (self.env.properties[self.for_machine].get('pkg_config_static', None) == 'true'):
              libcmd.append('--static')
          # Force pkg-config to output -L fields even if they are system
          # paths so we can do manual searching with cc.find_library() later.
 -- 
-2.24.1
+2.25.4