Add the .POSIX line to Makefile (#1928)

Signed-off-by: Ioannis Polyzos <git@ipolyzos.com>
Signed-off-by: Christian Mesh <christianmesh1@gmail.com>
Co-authored-by: Christian Mesh <christianmesh1@gmail.com>

CHANGELOG.md

@@ -13,6 +13,7 @@ ENHANCEMENTS:
 * Added multi-line support to the `tofu console` command. ([#1307](https://github.com/opentofu/opentofu/issues/1307))
 * Added a help target to the Makefile. ([#1925](https://github.com/opentofu/opentofu/pull/1925))
 * Added a simplified Build Process with a Makefile Target ([#1926](https://github.com/opentofu/opentofu/issues/1926))
+* Ensures that the Makefile adheres to POSIX standards ([#1811](https://github.com/opentofu/opentofu/pull/1928))
 * Added for-each support to providers. ([#300](https://github.com/opentofu/opentofu/issues/300))
 
 BUG FIXES:

Makefile

@@ -1,3 +1,5 @@
+.POSIX:
+
 export PATH := $(abspath bin/):${PATH}
 
 # Dependency versions