[Arm] Allow the use of arm_cde.h for C++

[Matthew Malcomson]

arm_cde.h includes the arm_mve_types.h header, which declares some C++
overloaded functions.

There is a superfluous `extern "C"` statement in arm_cde.h, which
encompasses these functions.  This means that if compiling for C++, the
overloaded functions are declared, but are declared without name
mangling.  Hence all the function names are the same and we have many
conflicting declarations.

Testing Done:
  Regression tested for arm-none-eabi.

gcc/ChangeLog:

2020-04-09  Matthew Malcomson  <matthew.malcom...@arm.com>

        * config/arm/arm_cde.h: Remove `extern "C"` when compiling for
        C++.

gcc/testsuite/ChangeLog:

2020-04-09  Matthew Malcomson  <matthew.malcom...@arm.com>

        * g++.target/arm/cde_mve.C: New test.



###############     Attachment also inlined for ease of reply    ###############


diff --git a/gcc/config/arm/arm_cde.h b/gcc/config/arm/arm_cde.h
index 
d8ddda6bd648d8b94e97f7b6403b7708cebc9eb3..0ba3ee02d057dd280c9b3400ef70b46ed472aec3
 100644
--- a/gcc/config/arm/arm_cde.h
+++ b/gcc/config/arm/arm_cde.h
@@ -27,10 +27,6 @@
 #ifndef _GCC_ARM_CDE_H
 #define _GCC_ARM_CDE_H 1
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 #include <stdint.h>
 
 #if defined (__ARM_FEATURE_CDE)
@@ -177,8 +173,4 @@ extern "C" {
 
 #endif
 
-#ifdef __cplusplus
-}
-#endif
-
 #endif
diff --git a/gcc/testsuite/g++.target/arm/cde_mve.C 
b/gcc/testsuite/g++.target/arm/cde_mve.C
new file mode 100644
index 
0000000000000000000000000000000000000000..897cbd2b8119471385c1c51158b1aa4851acbaf1
--- /dev/null
+++ b/gcc/testsuite/g++.target/arm/cde_mve.C
@@ -0,0 +1,10 @@
+/* { dg-do compile } */
+/* { dg-require-effective-target arm_v8_1m_main_cde_mve_fp_ok } */
+/* { dg-add-options arm_v8_1m_main_cde_mve_fp } */
+
+/* Ensure this compiles.  */
+#include "arm_cde.h"
+int foo ()
+{
+  return 1;
+}


diff --git a/gcc/config/arm/arm_cde.h b/gcc/config/arm/arm_cde.h
index 
d8ddda6bd648d8b94e97f7b6403b7708cebc9eb3..0ba3ee02d057dd280c9b3400ef70b46ed472aec3
 100644
--- a/gcc/config/arm/arm_cde.h
+++ b/gcc/config/arm/arm_cde.h
@@ -27,10 +27,6 @@
 #ifndef _GCC_ARM_CDE_H
 #define _GCC_ARM_CDE_H 1
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 #include <stdint.h>
 
 #if defined (__ARM_FEATURE_CDE)
@@ -177,8 +173,4 @@ extern "C" {
 
 #endif
 
-#ifdef __cplusplus
-}
-#endif
-
 #endif
diff --git a/gcc/testsuite/g++.target/arm/cde_mve.C 
b/gcc/testsuite/g++.target/arm/cde_mve.C
new file mode 100644
index 
0000000000000000000000000000000000000000..897cbd2b8119471385c1c51158b1aa4851acbaf1
--- /dev/null
+++ b/gcc/testsuite/g++.target/arm/cde_mve.C
@@ -0,0 +1,10 @@
+/* { dg-do compile } */
+/* { dg-require-effective-target arm_v8_1m_main_cde_mve_fp_ok } */
+/* { dg-add-options arm_v8_1m_main_cde_mve_fp } */
+
+/* Ensure this compiles.  */
+#include "arm_cde.h"
+int foo ()
+{
+  return 1;
+}