libffi: add patch for building with clang on power (#16855)

* libffi: add patch for building with '%clang target=power*'

* libffi: fix version of clang/power patch

var/spack/repos/builtin/packages/libffi/clang-powerpc-3.2.1.patch

@@ -0,0 +1,24 @@
+diff --git a/src/powerpc/linux64.S b/src/powerpc/linux64.S
+index d2acb70..921e9cb 100644
+--- a/src/powerpc/linux64.S
++++ b/src/powerpc/linux64.S
+@@ -83,6 +83,7 @@ ffi_call_LINUX64:
+ 	mr	%r4, %r1
+ # if defined _CALL_LINUX || _CALL_ELF == 2
+ 	bl	ffi_prep_args64
++	nop
+ # else
+ 	bl	.ffi_prep_args64
+ # endif
+diff --git a/src/powerpc/linux64_closure.S b/src/powerpc/linux64_closure.S
+index 97421a4..3c62d5f 100644
+--- a/src/powerpc/linux64_closure.S
++++ b/src/powerpc/linux64_closure.S
+@@ -152,6 +152,7 @@ ffi_closure_LINUX64:
+ 	# make the call
+ # if defined _CALL_LINUX || _CALL_ELF == 2
+ 	bl ffi_closure_helper_LINUX64
++	nop
+ # else
+ 	bl .ffi_closure_helper_LINUX64
+ # endif

var/spack/repos/builtin/packages/libffi/package.py

@@ -17,6 +17,8 @@ class Libffi(AutotoolsPackage, SourcewarePackage):
     version('3.3',   sha256='72fba7922703ddfa7a028d513ac15a85c8d54c8d67f55fa5a4802885dc652056')
     version('3.2.1', sha256='d06ebb8e1d9a22d19e38d63fdb83954253f39bedc5d46232a05645685722ca37')
 
+    patch('clang-powerpc-3.2.1.patch', when='@3.2.1%clang platform=linux')
+
     @property
     def headers(self):
         # The headers are probably in self.prefix.lib but we search everywhere