test: assert the host's quote character, not a fixed one

The Windows runner failed `LocalIncludeDirsWithSpacesAreShellQuoted` for a
difference that is correct: shell_quote_arg emits single quotes for POSIX sh
and double for cmd.exe, and the assertion hardcoded `'`. Both the unit test
and e2e 179 now take the quote character from the platform.

e2e 179 also drops its `unix-shell` requirement. Paths with spaces are the
Windows problem — `C:\Program Files`, an account name with a space — so
skipping the test there left the platform it exists for uncovered.

Author: Sunrisepeak

tests/e2e/179_spaced_paths.sh

@@ -1,5 +1,4 @@
 #!/usr/bin/env bash
-# requires: unix-shell
 # 179_spaced_paths.sh — a project whose paths contain spaces still builds
 #
 # #331: two independent places assumed no path ever contains a space. On
@@ -79,7 +78,11 @@ grep -q "vendor" "$ninja_file" || {
 # the shell quoting wraps the whole token (so what ninja hands to sh stays one
 # word). The old code had only the first, which is exactly why the path
 # survived ninja and then split in the shell.
-grep -qE "'-I[^']*vendor\\\$ inc" "$ninja_file" || {
+# The quote character is the host shell's — POSIX sh single, cmd.exe double —
+# so accept either rather than pinning whichever platform this happens to run
+# on. (An earlier version hardcoded `'` and failed on Windows for a difference
+# that was correct.)
+grep -qE "['\"]-I[^'\"]*vendor\\\$ inc" "$ninja_file" || {
     echo "FAIL: include dir not shell-quoted with its prefix:"
     grep -oE "[^ ]*vendor[^ ]*( inc[^ ]*)?" "$ninja_file" | head -3
     exit 1; }

tests/unit/test_ninja_backend.cpp

@@ -266,8 +266,13 @@ TEST(NinjaBackend, LocalIncludeDirsWithSpacesAreShellQuoted) {
     // only the first, which is why the path survived ninja and then split in
     // the shell. The prefix must be INSIDE the quotes — quoting the path
     // alone would leave `-I` as its own word and reintroduce the split.
-    EXPECT_NE(line.find("'-I/opt/my$ dep/include'"), std::string::npos) << line;
-    EXPECT_NE(line.find("'-idirafter/opt/my$ dep/after'"), std::string::npos) << line;
+    //
+    // The quote character is the host shell's, not a fixed one: POSIX sh
+    // wants single quotes, cmd.exe double. Hardcoding `'` passed on Linux
+    // and failed on the Windows runner for a difference that is correct.
+    const std::string q = mcpp::platform::is_windows ? "\"" : "'";
+    EXPECT_NE(line.find(q + "-I/opt/my$ dep/include" + q), std::string::npos) << line;
+    EXPECT_NE(line.find(q + "-idirafter/opt/my$ dep/after" + q), std::string::npos) << line;
 }
 
 // #261: on Windows $local_includes is copied into a RESPONSE FILE, which the