Fix the build on Solaris

If SHELL is set `make` fails on Solaris with:
mksh: Fatal error: Could not load Shell from `sh': Bad file number
Remove it so it builds.

Author: samcv

Configure.pl

@@ -147,7 +147,8 @@
     }
     $config{'makefile-timing'} = $options{'makefile-timing'};
     $config{'stagestats'} = '--stagestats' if $options{'makefile-timing'};
-    $config{'shell'} = $^O eq 'MSWin32' ? 'cmd' : 'sh';
+    my $shell = $^O eq 'MSWin32' ? 'cmd' : 'sh';
+    $config{'shell'} = $^O eq 'solaris' ? '' : "SHELL = $shell";
     $config{'bat'}   = $^O eq 'MSWin32' ? '.bat' : '';
     $config{'cpsep'} = $^O eq 'MSWin32' ? ';' : ':';
     $config{'slash'} = $slash;

tools/build/Makefile-common.in

@@ -113,7 +113,7 @@ CHMOD         = $(PERL) -MExtUtils::Command -e chmod
 CP            = $(PERL) -MExtUtils::Command -e cp
 RM_RF         = $(PERL) -MExtUtils::Command -e rm_rf
 RM_F          = $(PERL) -MExtUtils::Command -e rm_f
-SHELL         = @shell@
+@shell@
 
 SYSROOT         = @sysroot@
 PREFIX          = @prefix@