Fix finding the correct cplusplus compiler

ExtUtils::CBuilder was using a slightly maverick method for
finding the matching cplusplus compiler to the c compiler
used to build perl.

On a Linux system with a perl built with the Oracle Developer cc
cc='/opt/oracle/developerstudio12.6/bin/cc'

Errors were observed:
"c++: error: unrecognized command line option ‘-KPIC’; did you mean ‘-fPIC’?"

The cplusplus command for Oracle Developer suite is CC not c++ and the
detection was picking up the system c++ (g++).

If there is a ccpath, the code should exhaust all the options and not fail
through to using no path.

Added a test to exercise ccpath behaviour

Added clang/clang++ to the C->C++ compiler mappings

Author: bingos

dist/ExtUtils-CBuilder/lib/ExtUtils/CBuilder.pm

@@ -7,7 +7,7 @@ use Perl::OSType qw/os_type/;
 
 use warnings;
 use strict;
-our $VERSION = '0.280240'; # VERSION
+our $VERSION = '0.280241'; # VERSION
 our @ISA;
 
 # We only use this once - don't waste a symbol table entry on it.

dist/ExtUtils-CBuilder/lib/ExtUtils/CBuilder/Base.pm

@@ -9,7 +9,7 @@ use Text::ParseWords;
 use IPC::Cmd qw(can_run);
 use File::Temp qw(tempfile);
 
-our $VERSION = '0.280240'; # VERSION
+our $VERSION = '0.280241'; # VERSION
 
 # More details about C/C++ compilers:
 # http://developers.sun.com/sunstudio/documentation/product/compiler.jsp
@@ -24,6 +24,7 @@ my %cc2cxx = (
     xlc => [ 'xlC' ], # IBM C/C++ Set, xlc without thread-safety
     xlc_r => [ 'xlC_r' ], # IBM C/C++ Set, xlc with thread-safety
     cl    => [ 'cl' ], # Microsoft Visual Studio
+    clang => [ 'clang++' ], # LLVM compiler frontend
 );
 
 sub new {
@@ -51,24 +52,31 @@ sub new {
 
     ## If the path is just "cc", fileparse returns $ccpath as "./"
     $ccpath = "" if $self->{config}{cc} =~ /^\Q$ccbase$ccsfx\E$/;
-      
+
     foreach my $cxx (@{$cc2cxx{$ccbase}}) {
-      my $cxx1 = File::Spec->catfile( $ccpath, $cxx . $ccsfx);
 
-      if( can_run( $cxx1 ) ) {
-        $self->{config}{cxx} = $cxx1;
-	last;
-      }
-      my $cxx2 = $cxx . $ccsfx;
+      if ( $ccpath ) {
+          my $cxx1 = File::Spec->catfile( $ccpath, $cxx . $ccsfx);
+
+          if( can_run( $cxx1 ) ) {
+              $self->{config}{cxx} = $cxx1;
+              last;
+          }
 
-      if( can_run( $cxx2 ) ) {
-        $self->{config}{cxx} = $cxx2;
-	last;
       }
+      else {
+          my $cxx2 = $cxx . $ccsfx;
+
+          if( can_run( $cxx2 ) ) {
+              $self->{config}{cxx} = $cxx2;
+              last;
+          }
+
+          if( can_run( $cxx ) ) {
+              $self->{config}{cxx} = $cxx;
+              last;
+          }
 
-      if( can_run( $cxx ) ) {
-        $self->{config}{cxx} = $cxx;
-	last;
       }
     }
     unless ( exists $self->{config}{cxx} ) {

dist/ExtUtils-CBuilder/lib/ExtUtils/CBuilder/Platform/Unix.pm

@@ -4,7 +4,7 @@ use warnings;
 use strict;
 use ExtUtils::CBuilder::Base;
 
-our $VERSION = '0.280240'; # VERSION
+our $VERSION = '0.280241'; # VERSION
 our @ISA = qw(ExtUtils::CBuilder::Base);
 
 sub link_executable {

dist/ExtUtils-CBuilder/lib/ExtUtils/CBuilder/Platform/VMS.pm

@@ -4,7 +4,7 @@ use warnings;
 use strict;
 use ExtUtils::CBuilder::Base;
 
-our $VERSION = '0.280240'; # VERSION
+our $VERSION = '0.280241'; # VERSION
 our @ISA = qw(ExtUtils::CBuilder::Base);
 
 use File::Spec::Functions qw(catfile catdir);

dist/ExtUtils-CBuilder/lib/ExtUtils/CBuilder/Platform/Windows.pm

@@ -8,7 +8,7 @@ use File::Spec;
 use ExtUtils::CBuilder::Base;
 use IO::File;
 
-our $VERSION = '0.280240'; # VERSION
+our $VERSION = '0.280241'; # VERSION
 our @ISA = qw(ExtUtils::CBuilder::Base);
 
 =begin comment

dist/ExtUtils-CBuilder/lib/ExtUtils/CBuilder/Platform/Windows/BCC.pm

@@ -1,6 +1,6 @@
 package ExtUtils::CBuilder::Platform::Windows::BCC;
 
-our $VERSION = '0.280240'; # VERSION
+our $VERSION = '0.280241'; # VERSION
 
 use strict;
 use warnings;

dist/ExtUtils-CBuilder/lib/ExtUtils/CBuilder/Platform/Windows/GCC.pm

@@ -1,6 +1,6 @@
 package ExtUtils::CBuilder::Platform::Windows::GCC;
 
-our $VERSION = '0.280240'; # VERSION
+our $VERSION = '0.280241'; # VERSION
 
 use warnings;
 use strict;

dist/ExtUtils-CBuilder/lib/ExtUtils/CBuilder/Platform/Windows/MSVC.pm

@@ -1,6 +1,6 @@
 package ExtUtils::CBuilder::Platform::Windows::MSVC;
 
-our $VERSION = '0.280240'; # VERSION
+our $VERSION = '0.280241'; # VERSION
 
 use warnings;
 use strict;

dist/ExtUtils-CBuilder/lib/ExtUtils/CBuilder/Platform/aix.pm

@@ -5,7 +5,7 @@ use strict;
 use ExtUtils::CBuilder::Platform::Unix;
 use File::Spec;
 
-our $VERSION = '0.280240'; # VERSION
+our $VERSION = '0.280241'; # VERSION
 our @ISA = qw(ExtUtils::CBuilder::Platform::Unix);
 
 sub need_prelink { 1 }

dist/ExtUtils-CBuilder/lib/ExtUtils/CBuilder/Platform/android.pm

@@ -6,7 +6,7 @@ use File::Spec;
 use ExtUtils::CBuilder::Platform::Unix;
 use Config;
 
-our $VERSION = '0.280240'; # VERSION
+our $VERSION = '0.280241'; # VERSION
 our @ISA = qw(ExtUtils::CBuilder::Platform::Unix);
 
 # The Android linker will not recognize symbols from