DOC: fix some spelling issues over multiple files
This is from the output of codespell and may be backported.
diff --git a/INSTALL b/INSTALL
index 32cf5d9..32c0dd3 100644
--- a/INSTALL
+++ b/INSTALL
@@ -528,7 +528,7 @@
DEBUG_CFLAGS.
Building on AIX 7.2 works fine using the "aix72-gcc" TARGET. It adds two
-special CFLAGS to prevent the loading of AIXs xmem.h and var.h. This is done
+special CFLAGS to prevent the loading of AIX's xmem.h and var.h. This is done
by defining the corresponding include-guards _H_XMEM and _H_VAR. Without
excluding those header-files the build fails because of redefinition errors.
Furthermore, the atomic library is added to the LDFLAGS to allow for