Update installer with appveyor commands.

appveyor.yml

@@ -26,7 +26,9 @@ install:
     - refreshenv
     # We need to reload vcvars after refreshing
     - call "C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Auxiliary\Build\vcvars32.bat"
-    - build_win test-install
+    - build_win test-install\
+    - set janet_outname="%appveyor_repo_tag_name%"
+    - if "%janet_outname%"=="" (set janet_outname=v1.2.0)
 build: off
 
 only_commits:
@@ -44,11 +46,11 @@ artifacts:
     - name: janetconf.h
       path: dist\janetconf.h
       type: File
-    - name: "janet-$(appveyor_repo_tag_name)-windows"
+    - name: "janet-$(janet_outname)-windows"
       path: dist
       type: Zip
-    - path: "janet-$(appveyor_repo_tag_name)-windows-installer.exe"
-      name: "janet-$(appveyor_repo_tag_name)-windows-installer.exe"
+    - path: "janet-$(janet_outname)-windows-installer.exe"
+      name: "janet-$(janet_outname)-windows-installer.exe"
       type: File
 
 deploy:

janet-installer.nsi

@@ -25,7 +25,19 @@ VIFileVersion "${PRODUCT_VERSION}"
 
 # Basics
 Name "Janet"
-OutFile "janet-v${VERSION}-windows-installer.exe"
+
+# Do some NSIS-fu to figure out at compile time if we are in appveyor
+!define OUTNAME $%APPVEYOR_REPO_TAG_NAME%
+!define "CHECK_${OUTNAME}"
+!define DOLLAR "$"
+!ifdef CHECK_${DOLLAR}%APPVEYOR_REPO_TAG_NAME%
+    # We are not in the appveyor environment, use version name
+    !define OUTNAME_PART v${VERSION}-nonrelease-
+!else
+    # We are in appveyor, use git tag name for installer
+    !define OUTNAME_PART ${OUTNAME}
+!endif
+OutFile "janet-${OUTNAME_PART}-windows-installer.exe"
 
 # Some Configuration
 !define APPNAME "Janet"