Rename native code coverage paths product variables in Make.

Rename `CoveragePath` and `CoverageExcludePaths` as
`NativeCoveragePath` and `NativeCoverageExcludePaths` (resp.).
Also, populate `NativeCoveragePath` and `NativeCoverageExcludePaths`
from environment variables `NATIVE_COVERAGE_PATHS` and
`NATIVE_COVERAGE_EXCLUDE_PATHS` (resp.).

Test: m nothing
Bug: 158212027
Change-Id: I409dbb04b09744a7bd95a4b69361e858b9f89e23
diff --git a/core/line_coverage.mk b/core/line_coverage.mk
index 9b0b528..b920e28 100644
--- a/core/line_coverage.mk
+++ b/core/line_coverage.mk
@@ -9,7 +9,7 @@
 #
 # To run the make target set the coverage related envvars first:
 # 	NATIVE_LINE_COVERAGE=true NATIVE_COVERAGE=true \
-#	COVERAGE_PATHS=* make haiku-line-coverage
+#	NATIVE_COVERAGE_PATHS=* make haiku-line-coverage
 # -----------------------------------------------------------------
 
 # TODO(b/148306195): Due this issue some fuzz targets cannot be built with