Override cppcheck library & platform options (#691)

* Using LIBRARY=[avr|gnu] git cppcheck ... will set the command
   line library= to the value
 * Using PLATFORM=[avr.xml|unix32.xml] git cppcheck ... will set
   the command line platform= to the value
 * Corrected logical if error when bootstapping a pristine repo

References #672

.mystools/cppcheck/config/unix32.xml

@@ -0,0 +1,17 @@
+<?xml version="1.0"?>
+<platform>
+  <char_bit>8</char_bit>
+  <default-sign>unsigned</default-sign>
+  <sizeof>
+    <short>2</short>
+    <int>4</int>
+    <long>4</long>
+    <long-long>8</long-long>
+    <float>4</float>
+    <double>8</double>
+    <long-double>12</long-double>
+    <pointer>4</pointer>
+    <size_t>4</size_t>
+    <wchar_t>2</wchar_t>
+  </sizeof>
+</platform>

.mystools/cppcheck/options.sh

@@ -4,8 +4,8 @@ OPTIONS="--quiet                                      \
 	--error-exitcode=1                                  \
 	--force                                             \
 	--enable=style,information                          \
-	--library=avr                                       \
-	--platform="${TOOLCONFIG}"/avr.xml                  \
+	--library=${LIBRARY:-avr}                           \
+	--platform="${TOOLCONFIG}"/${PLATFORM:-avr.xml}     \
  	--includes-file="${TOOLCONFIG}"/includes.cfg	      \
 	--suppressions-list="${TOOLCONFIG}"/suppressions.cfg"