Have build scripts fail on first failing command

This avoids spurious errors from trying to copy files that weren't built,
and mimics the behavior of other build systems

src/subbuild-mac-intel.sh

@@ -1,5 +1,7 @@
 #!/bin/sh
 
+set -e
+
 # Default flags
 CMFLAGS="-D CMAKE_BUILD_TYPE:STRING=Release"
 

src/subbuild-unix-unix.sh

@@ -1,5 +1,7 @@
 #!/bin/sh
 
+set -e
+
 # Default flags
 CMFLAGS="-D CMAKE_BUILD_TYPE:STRING=Release"
 

src/subbuild-unix-w32.sh

@@ -1,5 +1,7 @@
 #!/bin/sh
 
+set -e 
+
 # Default flags
 CMFLAGS="-D CMAKE_BUILD_TYPE:STRING=Release"