Minor cleanups for install_llvm_module/uninstall_llvm_module Make macros.

Don't put comments inside the macros, per complaint from Michael Paquier.

Quote target directory path with single quotes, not double; that seems
to be our project standard.  Not quoting it at all definitely isn't
per standard.

Remove excess slash in one instance of path.

Remove useless semicolon.

Discussion: https://postgr.es/m/20180428073935.GB1736@paquier.xyz

src/Makefile.global.in

@@ -1017,19 +1017,14 @@ endif
 # $(1) name of the module (e.g. an extension's name or postgres for core code)
 # $(2) source objects, with .o suffix
 #
-define install_llvm_module
-# Create target directory
-$(MKDIR_P) "$(DESTDIR)${bitcodedir}/$(1)"
-# Create sub-directories, if files are in subdirectories
-$(MKDIR_P) $(sort $(dir $(addprefix $(DESTDIR)${bitcodedir}/$(1)/, $(2))))
-# Then install files
-#
 # The many INSTALL_DATA invocations aren't particularly fast, it'd be
 # good if we could coalesce them, but I didn't find a good way.
-$(foreach obj, ${2}, $(INSTALL_DATA) $(patsubst %.o,%.bc, $(obj)) $(DESTDIR)/${bitcodedir}/$(1)/$(dir $(obj));
+define install_llvm_module
+$(MKDIR_P) '$(DESTDIR)${bitcodedir}/$(1)'
+$(MKDIR_P) $(sort $(dir $(addprefix '$(DESTDIR)${bitcodedir}'/$(1)/, $(2))))
+$(foreach obj, ${2}, $(INSTALL_DATA) $(patsubst %.o,%.bc, $(obj)) '$(DESTDIR)${bitcodedir}'/$(1)/$(dir $(obj))
 )
-# and generate index
-(cd "$(DESTDIR)${bitcodedir}" && $(LLVM_BINPATH)/llvm-lto -thinlto -thinlto-action=thinlink -o $(1).index.bc $(addprefix $(1)/,$(patsubst %.o,%.bc, $(2))))
+cd '$(DESTDIR)${bitcodedir}' && $(LLVM_BINPATH)/llvm-lto -thinlto -thinlto-action=thinlink -o $(1).index.bc $(addprefix $(1)/,$(patsubst %.o,%.bc, $(2)))
 endef
 
 # Uninstall LLVM bitcode module.
@@ -1040,6 +1035,6 @@ endef
 # This intentionally doesn't use the explicit installed file list,
 # seems too likely to change regularly.
 define uninstall_llvm_module
-rm -rf "$(DESTDIR)${bitcodedir}/$(1)/"
-rm -f "$(DESTDIR)${bitcodedir}/$(1).index.bc"
+rm -rf '$(DESTDIR)${bitcodedir}/$(1)/'
+rm -f '$(DESTDIR)${bitcodedir}/$(1).index.bc'
 endef