Fix build systems with preset environment (Artix)

Signed-off-by: Страхиња Радић <contact@strahinja.org>

.SRCINFO

@@ -1,7 +1,7 @@
 pkgbase = sled
 	pkgdesc = Simple text editor
 	pkgver = 0.12.7
-	pkgrel = 1
+	pkgrel = 2
 	url = https://strahinja.srht.site/sled
 	arch = x86_64
 	license = GPL3

PKGBUILD

@@ -1,7 +1,7 @@
 # Maintainer: Strahinya Radich <contact@strahinja.org>
 pkgname=sled
 pkgver=0.12.7
-pkgrel=1
+pkgrel=2
 pkgdesc="Simple text editor"
 arch=('x86_64')
 url="https://strahinja.srht.site/sled"
@@ -21,10 +21,20 @@ build() {
 	# (uncomment next line)
 	#sed -i 's,^\(#define ENABLE_WRAP\),//\1,' config.h
 
+	# Some build environments insist on having those preset, which breaks
+	# the build; if you really want some of them, comment the 'unset' lines
+	# below, but note you are on your own wrt errors.
+	unset BINDIR CC CFLAGS CPPFLAGS DOCDIR HEADERS INSTALL LDFLAGS LIBS
+	unset MANPAGE MANPREFIX OBJS PROG SRC 
+
 	FALLBACKVER=$pkgver-$pkgrel PREFIX="$pkgdir/usr" make -e all
 }
 
 package() {
 	cd $pkgname-v$pkgver
+
+	unset BINDIR CC CFLAGS CPPFLAGS DOCDIR HEADERS INSTALL LDFLAGS LIBS
+	unset MANPAGE MANPREFIX OBJS PROG SRC 
+
 	FALLBACKVER=$pkgver-$pkgrel PREFIX="$pkgdir/usr" make -e install
 }