Add environ as a link seam for platform APIs

Allow precise redirection of platform-related APIs (such as those
provided by libc) for the purpose of unit tests.

Change-Id: I615b25805fc7a24eb5d67e87237bf35c8e262b93
Signed-off-by: Amithash Prasad <amithash@meta.com>
Signed-off-by: Andrew Jeffery <andrew@codeconstruct.com.au>
diff --git a/src/meson.build b/src/meson.build
index 13f7d9e..c49d1bb 100644
--- a/src/meson.build
+++ b/src/meson.build
@@ -16,6 +16,7 @@
 endif
 
 subdir('firmware_device')
+subdir('environ')
 
 libpldm_link_args = []
 foreach alias : libpldm_deprecated_aliases