cc-wrapper: Use separate mangler for "bool" variables

This avoids any `NIX_FOOBAR=1 1` not triggering conditions.

pkgs/build-support/cc-wrapper/add-flags.sh

@@ -4,7 +4,7 @@
 # that case, it is cheaper/better to not repeat this step and let the forked
 # wrapped binary just inherit the work of the forker's wrapper script.
 
-var_templates=(
+var_templates_list=(
     NIX+CFLAGS_COMPILE
     NIX+CFLAGS_LINK
     NIX+CXXSTDLIB_COMPILE
@@ -14,7 +14,9 @@ var_templates=(
     NIX+LDFLAGS
     NIX+LDFLAGS_BEFORE
     NIX+LDFLAGS_AFTER
+)
 
+var_templates_bool=(
     NIX+SET_BUILD_ID
     NIX+DONT_SET_RPATH
     NIX+ENFORCE_NO_NATIVE
@@ -35,9 +37,12 @@ fi
 
 # We need to mangle names for hygiene, but also take parameters/overrides
 # from the environment.
-for var in "${var_templates[@]}"; do
+for var in "${var_templates_list[@]}"; do
     mangleVarList "$var" "${role_infixes[@]}"
 done
+for var in "${var_templates_bool[@]}"; do
+    mangleVarBool "$var" "${role_infixes[@]}"
+done
 
 # `-B@out@/bin' forces cc to use ld-wrapper.sh when calling ld.
 NIX_@infixSalt@_CFLAGS_COMPILE="-B@out@/bin/ $NIX_@infixSalt@_CFLAGS_COMPILE"

pkgs/build-support/cc-wrapper/utils.sh

@@ -1,20 +1,35 @@
 mangleVarList() {
-    declare var="$1"
+    local var="$1"
     shift
-    declare -a role_infixes=("$@")
+    local -a role_infixes=("$@")
 
-    outputVar="${var/+/_@infixSalt@_}"
-    export ${outputVar}+=''
+    local outputVar="${var/+/_@infixSalt@_}"
+    declare -gx ${outputVar}+=''
     # For each role we serve, we accumulate the input parameters into our own
     # cc-wrapper-derivation-specific environment variables.
     for infix in "${role_infixes[@]}"; do
-        inputVar="${var/+/${infix}}"
+        local inputVar="${var/+/${infix}}"
         if [ -v "$inputVar" ]; then
             export ${outputVar}+="${!outputVar:+ }${!inputVar}"
         fi
     done
 }
 
+mangleVarBool() {
+    local var="$1"
+    shift
+    local -a role_infixes=("$@")
+
+    local outputVar="${var/+/_@infixSalt@_}"
+    declare -gxi ${outputVar}+=0
+    for infix in "${role_infixes[@]}"; do
+        local inputVar="${var/+/${infix}}"
+        if [ -v "$inputVar" ]; then
+            let "${outputVar} |= ${!inputVar}"
+        fi
+    done
+}
+
 skip () {
     if (( "${NIX_DEBUG:-0}" >= 1 )); then
         echo "skipping impure path $1" >&2